It is often the case that hidden file corruption is tolerated by one version of FileMaker or one OS but not others. Likely your file was already damaged, but 8.5 'tolerated' it.
Did the recovered file work?
Things to keep in mind about Recover:
- Recover does not detect all problems
- Recover doesn't always fix all problems correctly
- Best Practice is to never put a recovered copy back into regular use or development. Instead, replace the damaged file with an undamaged back up copy if this is at all possible. You may have to save a clone of the back up copy and import all data from your recovered copy to get a working copy with the most up to date information possible.