I don't know that there's any limit. I don't often use Pages, but I have had documents with many more than 52 Comments.
Simple things to try (of course a reminder, back up your work)––
Start up Pages app while pressing the Shift key before opening the problematic document:
"Press and hold the Shift key while opening the app. This doesn't change any settings, but the app forgets any windows that were open the last time you quit the app."
Prevent apps and windows from reopening on Mac - Apple Support
Start up your computer in Safe Mode, test, then start in Normal Mode. Just the act of starting in Safe Mode then Normal can clear issues:
"Safe mode prevents your Mac from loading certain software as it starts up, including login items, system extensions not required by macOS, and fonts not installed by macOS. It also does a basic check of your startup disk, similar to using First Aid in Disk Utility. And it deletes some system caches, including font caches and the kernel cache, which are automatically created again as needed."
How to use safe mode on your Mac - Apple Support
As I said, I'm an infrequent Pages user but if I had to and faced a looming deadline, after trying the above without success, I'd resort to copying/pasting sections and/or the entire manuscript into a new document (the original could be corrupted in some fashion).
Finally, again with a deadline in mind, use a simple workaround such as track changes to colorfully note potential edits. A bothersome change of habit but work sometimes can't wait for a technical issue to be resolved.
Best....
[Edit to add––I didn't see @jmarse1's advice before posting.]