Try running a recover on the file to check it for damage. If this is a hosted file, run the recover on a recent back up copy.
It's not unheard of for latent (hidden) file damage to produce no observable issues with a file (that's why we call it 'Latent'), until either the OS or FileMaker is upgraded to a new version, then some difference in versions results in a crash or other strange behavior.
Even if you don't get a report of any problems found by the recover, test the recovered copy to see if it still crashes on you.
Phil, Will do. Thanks
Fred, Did it. Thanks, Pat