InDesign 2025/2026 freezing (not responding) with Paragraph Panel & multiple CEP HTML Engine instances, with possible file corruption

After two technical support sessions and further testing, there is a relatively simple workaround, though not an actual solution to the problem, which is to reconstruct the affected files* (files that, according to the second tech support agent, don’t actually seem to be corrupted at all, though that remains unconfirmed):

First, the “solution”: moving pages from the problematic document to a new one

Though part of the issue is that both newer and older files, including incremental backups, can be at risk of being affected, and that the number of files that worked flawlessly before and that now present issues is too high to blame it on occasional file corruption, it is quite fortunate that reconstructing them is a relatively quick process, including moving master pages, and preserving the threads between text frames of different pages. And though it is important to emphasize that the actual cause of the problem is still unknown, at least the following steps worked for being able to make usable copies of the problematic files, given that brand new files (that might, maybe, get corrupted in the future, as it happened with newer ones), as of now, have not presented issues.

To do so, create a new document with the exact same measurements and margins based on the values in document setup, margins and columns, baseline grid settings, etc. Then, with both the new and old document open, move the master pages from the old document to the new one using the Move Pages command in the Pages panel before moving the pages with the actual contents of your original document.

This does not guarantee that the problem won’t eventually manifest on the new, rebuilt files but, at least, the ones I tested this with present no issues so far.

Second, latest tests and further context

First tech support session. Accessing the %appdata% folder in File Explorer by typing %appdata% directly into the address bar and, after entering the Adobe folder, deleting the corresponding InDesign preferences folder, for some reason, “worked” just once; after freezing for one last time for around a minute, the file seemed to work properly, but this option, despite being reproduced exactly, step by step, did not work at all afterwards; reproducing this proposed solution didn’t have any effect at all.

Second tech support session. The GPU acceleration wasn’t an issue, and the proposed solution was moving the pages but, apart from that, I was told that the reason why these files seem to be causing issues “is probably because of a known windows update issue”: given that Windows 10 has reached end of support, “the crucial updates that help the OS communicate with the app and tell it how to handle files, is not functioning properly [… and] the moment you open the same file elsewhere, it refreshes the cache and the processes and thus, the file opens easily afterwards”. Furthermore, I was told: “I honestly don't think your files are getting corrupted actually. More like the way they are handled is confusing the application due to the outdated OS”. The Adobe agent also checked in the live session, using Command Prompt, the KB Windows Update numbers, and kindly provided me with installers for previous versions of InDesign for me to test, later, if a rollback would work.

Further testing

Unfortunately, the rollback option did not work, not only because some files were newer than the versions in question, but also because older files (in relation to the tested versions) kept presenting issues.

And after that, I tested the problematic files in Windows 11, on yet another computer, apart from the two that I already made tests with but that have Windows 10. It didn’t work, either. Technically, it could be posited that using W11 would prevent the issue from being further generated, but that kind of testing is beyond my current capabilities and time constraints, especially given that the problem at hand is of an unpredictable nature.

Conclusion

I’ll consider this issue only sufficiently resolved, because though a workaround has been found, all of my initial questions remain unanswered, and the problem itself has not actually been fixed, but avoided. The only thing left that is important to mention is that I noticed, upon seeing the Task Manager with the rebuilt files open, that the CEP HTML Engine is nowhere to be seen:

I hope this helps.

* Push damaged pages into a new file (from Mike Witherell’s troubleshooting guide):

https://community.adobe.com/questions%2D671/reset%2Dindesign%2Dpreferences%2Dand%2Dother%2Dtroubleshooting%2D867226