Ok, for everyone who is having this issue, here are the steps I was given by Adobe Support to solve for it (for macOS users):

- Quit out of all Adobe programs and Creative Cloud
- With Finder active, use the top menu to select Go and choose "Go to Folder..."
- Enter "~/library"
- Go to Preferences > Adobe InDesign and rename the "Version <number>" folder and rename it to "Version.Old.2"
- Go back to the ~/library folder and go to Caches > Adobe InDesign, and rename the "Version <number>" folder to "Version.Old"
- Reopen InDesign. It will make a new Version folder in each of those locations automatically.

This will cause you to lose your preferences and Workspaces though. You can recover that information by copying the related files from the Version.Old2 folder in Preferences. For instance, I copied my Workspace files (<Workspace Name>_CurrentWorkspace.xml and <Workspace Name>.xml into the new Version folder and after restarting InDesign, the Workspace was back. Scripts and other folders are also inside that Preferences folder.

Give this a shot if you are having this issue. It worked for me, but if it doesn't work for you, you can always copy all of the files from the Version.Old2 and Version.Old folders, paste them into the new ones, and delete the old and it'll put everything back where it was.

Undo is now exhibiting this behavior for me. I've never seen this happen before, and it just started today. Not only is it reverting back to the last saved version when I undo, but if I redo, it doesn't even restore all of the changes I made, only some.

This has so far cost me about 45 minutes of work today alone. I'm really losing patience with Adobe products. InDesign, Illustrator, and Photoshop have been crashing multiple times each day for seemingly no reason, and so far Adobe's support has been abysmal and done next to nothing to help solve the issue. What am I paying for each month?

same here! undo isnt working

Today it started again to be unusable. Same "undo"-problem again, really annoying!

Are we paying for the beta version? Absolutely not understandable.

Das ist voll lästig - was kann ich dagegen tun? Extreme Fehlerquelle!!!!

Undo is still not working for one step, and it also crashes frequently. Please HELP !!!

NOT WORKING. And I just updated it. What's happening with Adobe apps lately?

My InDesign is fully up to date and I am having this same problem consistently. So, no, I would not say it is "fixed."

Just tried out the update. Everything seems to be working fine. Thank you!

Is this fixed for Windows? The summary of fixes posted on Adobe's site says it was fixed on Mac

I will continue to use the previous version until I see evidence that this problem has been fixed. Part of that evidence (beside the glad cries of happy customers) would be the release of the new version, not a beta! I'm not paying for a beta, but a properly functioning piece of software... let's go ADOBE!!

I had the same problem. Very annoying. Then I tried deleting InDesign preferences and relaunching ID, and the problem seems to have gone away:
Solution found at https://community.adobe.com/t5/indesign/sos-indesign-won-t-save-save-as-and-i-can-t-undo/m-p/10866948?page=1

Adobe, please. When will this fix for the Undo bug be out of beta? The current application behavior is UNACCEPTABLE.

@Tony Seddon, thank you for the brilliant idea of changing my keyboard commands. It IS impossible to break the habit.

One thing I did to help the current situation is to remove the CMD+Z keystroke from Undo using Edit > Keyboard Shortcuts… At least then when you automatically hit CMD+Z (it's impossible to get out of the habit, right?) nothing happens and you can avoid losing a bunch of changes. I'm pretty sure it's saved me a lot of time. Fingers crossed that a full update happens soon - there's no way I'm using a Beta for live client projects.

Does anyone else see the irony of 'upgrading to a beta build'. I don't want to find more problems as adobe 'stabilizes' the platform.

I don't want to be a test rat… I want the stable platform that I pay for. The function worked (always worked and we depend on it), now the function doesn't work.

What's worse than simply losing time, is losing all the live changes I've made. I proofread in InDesign. How am I supposed to remember every little change I've made in the last ten minutes??

Same. It is MORE than frustrating!

Yeah, this is really frustrating. I have a team of people all suffering from this. Losing lots of time over here.

Is there any indication when this will be released from Beta as a full commercial release. Tempting as it is to download the Beta build, I'm not too keen on using it for actual work.