There are some tips here:
It is frustrating. I have a client that gets periodic "beachball" pauses with FM 10 Server, but can't find the cause
save a copy as compacted
run Recover, and check the log for items "changed"
> I've tried everything to recreate the issue and can't get it to run slow or crash. I wondered whether it's due to the age of their desktop machine rather than any filemaker issue but their IT manager says not!
I hadn't thought of recovering a saved compacted copy. I'll try that