The "+ mention" text does not appear when adding a comment for some documents

Normally when adding a comment to a doc the hint you get is “+Mention will provide…”
but with some document the +Mention hint does not appear and even if you type the + key the function “onRequestUsers” is not called. You can see that for certain documents the hint does not appear like this:
image. I think there is a bug that does not allowed certain document to access the hint text and the other methods to get the list of users. document server version 6.4

Hello @isaza00
I believe it’s better to troubleshoot the situation on the latest versions of product. Is it possible to update Document server to v.7.2.1 and double-check the issue?
NB! Please prepare whole server backup before update process just in case.