Just updated to ID 2020 15.1 and found a bug which makes the program unusable forcing me to immediately downgrade.
When I open on of my ID documents created in previous version of ID, all of my defined text variables as well as page numbers are corrupted and replaced by the "ss" text. Changing the style has no effect. I can create page number based on the 'Basic Paragraph' style but when i choose any other previously created style, the number changes to 'ss'.
Even the variable field preview shows 'ss' text instead of variable name.
The same document opens in ID 2020 15.0.3 without any problems.

Hi developers,
this is a longstanding bug:

With facing pages documents on EVERY document page there is a zone where jumping of objects will happen.

I call this the jump zone. All objects on a page that will jump are clearly inside the page's area. The bug has nothing to do with rounding errors where object edges are at the edge of a page.

The objects should not move if pages are added or removed, if numbering of pages is changing. Nevertheless they do. Always. Unless, the zone has a width of zero.

Below all the details.

What is a jump zone?
If horizontal values for left and right margins differ, there is a BUG that in effect forms a zone on the page.
I call this zone JUMP ZONE because objects that touch the zone with their edges could jump horizontally.

When will objects jump?
1. When a left-hand page becomes a right-hand page OR a right-hand page becomes a left-hand page.

1. When a left-hand page becomes a right-hand page and later when a right-hand page becomes a left-hand page again.

This could happen within a single InDesign document open.

WARNING:
It could even happen to InDesign documents that are not visibly open.
That's with InDesign documents that are part of a InDesign book file.
The book file's feature with auto-numbering pages can do this even if no document is visibly open.
The damage is done if auto-numbering took place AND the book file is saved.

How large is the jump zone?
The height of the zone is the height of the page.
The width of the zone can be calculated:
inner margin MINUS outer margin

How large is the jump?
The width of the jump zone.

Where is the jump zone positioned?
Positive value: The zone is at the spine of the page.
Objects that touch the zone jump towards the spine.

Negative value: The zone is at the edge of a page away from the spine.
Objects that touch the zone jump away from spine.

What versions of InDesign are affected?
All versions CC up to InDesign 2020, Mac OS X and Windows.
InDesign CS6, Mac OS X and Windows.

Possibly also InDesign CS5 and CS5.5, Mac OS X and Windows.
I did not test this.

How can I avoid jump zones?
Make right and left margin values the same!

Are there workarounds if I cannot avoid jump zones?

1. Anchor objects
   that touch the jump zone to text frames that do not touch the jump zone.
   Nested objects will not jump if the parent objects are not touching the jump zone.

2. Group an object
   to another one that is touching the top or the bottom edge of the page.
   Tests are showing that objects will not jump if they touch the bottom OR the top of the page.
   ( OR both, bottom and top edges of the page .)

Other things to consider about moving objects?
The following is independently of jump zones:
Objects could move to other pages if their edges touch exactly the horizontal edges on pages in facing pages.
Depending on the version of InDesign this could also happen with objects touching the spine.
Reason: Rounding errors.

What can provoke all this?
1. Add or remove an odd number of pages
so that left-hand pages become right-hand pages and vice versa.

1. Renumber start pages of sections so that left-hand pages become right-hand pages and vice versa.

Note:
Every document has at least one section by default.
The start of that section is the first page in the document.

More details at Adobe InDesign Forum:
https://community.adobe.com/t5/indesign/bug-in-book-s-update-numbering-feature/m-p/10774458#M166408

InDesign 2020 documents attached here.
See screenshots and further comments at Adobe InDesign Forum:
https://community.adobe.com/t5/indesign/bug-in-book-s-update-numbering-feature/m-p/10774596#M166420

Download link to all test files on my Dropbox account:
https://www.dropbox.com/s/duov096cu2q481l/Jump-Zones-Explained-Facing-Pages-Documents.zip?dl=0

Regards,
Uwe Laubender

( ACP )

PS: Why does InDesign Uservoice not permit to attach files with suffix .indd ?
Message: "Invalid file type: .indd files not allowed."
Isn't that rather absurd?

When we create new documents with facing pages and Primary Text Frames on, new master pages are then created based on that original master page.

I would expect them to inherit the same threading and Primary Text Frame designation as the original, but they don't. Only the text frame on the right hand master page is designated as part of the primary text flow, and the frames are no longer threaded. Designers have to check every based-on master, re-designate the primary text flow, and re-thread the frames.

The steps to reproduce are:
1. Create a new document with Facing Pages and Primary Text Frames enabled. The A-Master spread has primary text frames on each page, threaded together.

1. Create a new master that is based on the A-Master. The new master spread only inherits the Primary Text Frame on the right hand page. The page on the left gets a basic text frame, and the frames are not threaded across the spread.

I report a bug regarding an InDesign document of an anomalous character that is found in the "Story editor", which has already been reported in older versions of Adobe Indesign.
(OS version: BigSur 11.3.1)
(Adobe InDesign version: 16.2)

As you can see in the examples that I attach, the text presents problems and I believe it is caused (or highlighted) by the missing glyph signs in each line of the "story editor", which does not appear to exist in the text.

The problem is not solved by making the file idml.
I tried to fix it by copying the text and placing it in a new InDesign file, the result didn't change.
Then I tried to paste the text into "Microsoft Word" and after copying it again I brought it to a new InDesign file and, in that case, the problem disappears (unfortunately, however, I cannot do it with the entire text of the book because it is too complex and I'd basically have to start the job all over again). So I think the bug is only referable to certain files.

I also tried to create a new document by importing all the pages from the old one, but even this operation did not solve the problem.
In addition to this anomaly, I also noticed that clicking in some places of the text (to insert text or delete it manually) the cursor is positioned more and more to the left of where I click (for example, if I click after the last letter of the word after which I want to insert a text, the cursor is positioned between the penultimate and the last letter of that word, it is very annoying on a long job).

The same thing happened to my colleague in the department: another document caused many more problems than mine, especially on a certain page, whatever action he performed, the file often slowed down until the program was closed, it was very difficult for him to complete a job that was now in its final phase.

Finally, as described at the beginning, I point out the links of the posts where this problem has already been reported:

2018:
https://community.adobe.com/t5/indesign/first-character-of-story-editor-and-notes-panel-displays-incorrectly/td-p/9549599/page/2

2020:
https://indesign.uservoice.com/forums/601180-adobe-indesign-bugs

Say I have a two-page master, with facing pages turned on.
And say I have a rectangle spanning the top edge of my left page, and say the right page is empty.

When I apply this master to a right sided page (thus using only the right side master), the left rectangle will be rendered onto the left page, even though it shouldn't (as the rectangle belongs to the left handed master, which isn't applied).

This happens when the rectangle is touching the spine, and it's probably rendered by indesign as being part of the right master.
This happens even when the reference point of the rectangle is changed to be on the far side (with regard to the spine).

This is usually fixed by moving the rectangle a point away from the spine, but from searching online it seems like it doesn't always fix it. Moreover, this "fix" is still bad and serves as a bad-practice patch.

This appears to exist for a few years now, and all the answers to this topic are "we released an update", that obviously didn't solve the problem.

Thanks!