After upgrading to XWiki 18.1.0 the side menu to the left is disappearing after some navigation thru sides in the wiki. The hamburger menu at the top right is neither opening anymore then.
After restarting the tomcat service it works fine again for a while.
How can I track down the cause?
Thanks,
Chris
Hello, I can’t help you directly, but I think it might help, if you provide context. The people who might be able to help you need to know what is your setup 
My setup:
Hello,
Have you found a solution since last month?
I have upgraded to Debian 13 juste about 10 days ago or so, perhaps having several OpenJDK would not be so great to have.
What about doing a backup of your “data” directory and your database, and perhaps a snapshot too, if you can, then remove OpenJDK 11 and 17 packages? (Only 21 is needed in Debian 13, if your XWiki version is the lastest stable).
About errors, I had noticed the XWiki install was really slow, sluggish, unresponsive, after upgrading to Debian 13, and I decided to get help from an AI.
This how I looked for errors using its help (in a root console using journalct, and, I kept notes):
journalctl -u xwiki --no-pager --since "2026-03-01" | grep -i "WARN\|ERROR\|Exception" | grep -v "at org\." | grep -v "at com\." | grep -v "at java\." | head -50
If you want to use it, you would have to adapt (the date for one).
Then, this error appeared, in the output, on all pages, including the Main page:
ERROR - Left side ($unlicensedSheets.size()) of comparison operation
has null value at xwiki:Licenses.Code.MissingLicensesUIX[line 5, column 61]
So in my case the issue was coming from the licence manager. Once uninstalled from the extension manager, this issue was solved (other improvements had to be done, so I worked on that too).
I am not saying that your issue is the same as was mine, just that if you have not yet solved it, the method I used could perhaps help you get through it.