It sounds like you have one or more corrupted fonts on the misbehaving Mac. Use FontBook to replace them from one of the Macs that's acting right and see if that fixes the issue.
Thanks Mike! I tried this and it did not work. Any other suggestions?
Was this file converted from .fp7 format?
I think you did what should have been done.
How often do these Macs reboot? A reboot may have been just as beneficial as taking it off line, etc.
How many outhouse apps do the people download. Etc.
How much free memory is available to Filemaker? If you are using a dozen different apps and opening many different Windows, Filemaker may act up. If you have 25 windows open in Filemaker, it may choke.
Does it conflict with another app? I found that on my Dell laptop, Filemaker and the Chrome browser would not work well together.
Try opening activity monitor and view all of the things going on.
Then of course the old old question. What version of FIlemaker? Do you do the updates regularly. Here's a secret: all software is beta. We pay to be beta testers. The v1 of any database is something to avoid. For 12 you should be using v4.