Then the permission check Function is returning FALSE... if I had to guess, its the time limit permission.
That is not the only permission involved. There is a Time limit on editing/deleting own comments permissions.
View attachment 10840
Use the permissions check analyzer on one of the specific users. It will tell you what the final values are for BOTH of those permissions.
This works the same as Posts in a Thread that have a time limit permission.
Also, double check Category Permissions. AMS has a Category Permissions Analyzer, just like XF has a Node Permissions Analyzer.