It happens to me in Hebrew text:

Thank you for looking into this at last. As far as I can see, the spacing problem within a paragraph is caused by the use of certain white space characters that are available under Insert White Space – particularly the Thin Space and the Hair Space – and of the Discretionary Line Break. Not only are strings of Hebrew characters affected but also strings of Latin characters in that paragraph.

In 1_bad.png, twice a wide space prefixed and suffixed by a Discretionary Line Break is used – before "1." on the first line and before "2." on the second line. You can see that this affects the spacing of the Hebrew characters as well as some of the Latin ones, and some digits.

The problem is resolved when the Discretionary Line Break is removed, as in 2_good.png.

Please note that using the Adobe World-Ready Paragraph Composer is imperative if a string of RTL language characters needs to be displayed. Please also note that in certain circumstances, Discretionary Line Break characters or any of the white space characters mentioned above need the be used and cannot simply be omitted.

For what it's worth, the workaround described in reply 14 here https://forums.adobe.com/thread/1673064 works for me.

This serious bug is not yet solved in InDesign CS 2019:
<https://www.dropbox.com/s/cx39ktwpz51q1cq/cp_2019-03-18_01-02-51_PM2.png?dl=0>

I cannot remember this bug in InDesign ME up to CS5, developed by winsoft.fr.

To prevent from this bug I still have to typeset books and magazines in InDesign CS4(!).
It's a question of time that the old iMac with the old OS (Yosemite) stops running and doing this job.

Please solve this annoying bug in any time soon.

Regards
Martin

"When will Adobe address this."
Since this bug report is labeled with "NEED MORE INFO" I suggest, that everyone who is affected will join InDesign Prerelease and providing documents where the bug is visible there. Unfortunately we cannot upload samples or screenshots while commenting here…

Also note this new thread at Adobe InDesign Forum:

RTL + LTR lang in one paragraph with justification
annahayat Mar 17, 2019

https://forums.adobe.com/thread/2605107

Regards,
Uwe Laubender
(ACP)

This is a serious bug that has been evident for years and still is present in CC2019. When will Adobe address this.

Hello Uwe

Just getting back to this after being overwhelmed with work. Thanks for the links. I'm relieved to know that other people are having the same problem, but I'm disappointed that Adobe seems not to care.

I have done some more testing by changing preferences, changing paragraph settings, changing character settings, monkeying with saving memory, changing display performance—all to no avail. I too at one time thought that the discretionary line break triggers the bug, but after my latest testing, I'm pretty confident that it does not. Like one of the posters in the threads you provided, I am convinced the that bug is a recomposition problem. InDesign is simply giving up before it finishes composing the text.

Incomplete recomposition seems to be the underlying cause of two additional bugs that I have reported: Left indents at the top of a page are sometimes not honored until you force InDesign to recompose all stories, and preferences for rules above split footnotes are sometimes not honored after the footnote flow is changed until you open up the footnotes options dialog and change the rule settings, which seems to cause InDesign to reevaluate the treatment of all of the footnotes in the document.

About half of the books I typeset now have Hebrew or Arabic in them, and this bug is just so frustrating. If there were a viable workaround, it wouldn't be so bad, but there's just nothing effective. I have tried converting the Hebrew and Arabic to outlines, but as another poster pointed out, where the text includes a Hebrew or Arabic phrase—vs. an isolated word—this can create more serious problems, so I've abandoned that workaround.

I hope that Adobe eventually decides to fix errors in the existing version of the program before focusing their attention on new features. I finally caved in to the subscription model (which I still detest) mostly because I was hoping that they would update the program with bug fixes on a monthly basis and would eventually fix this one. Sigh.

Anyway, thanks again. I'll keep trying to find a fix as time allows.

m.

Hi Matthew,
at least for me and some others this is a known bug we already see in earlier versions of InDesign. I have some samples with e.g. CS6 8.1.0.

See this discussion in German at hilfdirselbst.ch where Martin Fischer is seeing the issue:
https://www.hilfdirselbst.ch/foren/Globaler_Adobe_Absatzsetzer%3A_unerw%FCnschte_Spationierungen_an_zuf%E4lligen_Stellen_P551491.html#551491

Or at the same site this one here:
https://www.hilfdirselbst.ch/foren/Hebr%E4ische_Buchstaben_laufen_verkehrt_herum_P539208.html#539208

Also did a crosslink to this report here.

Thanks,
Uwe Laubender
( ACP )

Still nothing more than a month later. Not even an acknowledgment. What a shame. The only solution I have available right now is to convert the Hebrew and Arabic to outlines, turn off World-Ready Paragraph Composer, and hope no one has any edits to the Hebrew or Arabic or to the English text that might cause the Hebrew or Arabic to line break. This is not a nuisance or a "wouldn't it be nice if" report. This is a major behavior problem when setting mixed-direction text, but apparently, Adobe can't be bothered. It's like I'm reliving my Quark days. Sigh.

Just checking in to see what response my question has had. :-(