Product and version: FM 17.0.1
OS and version: Mac 10.12.6
Double-clicking a .fmp12 file in the Finder, opens it in an older version rather than in FM 17, in my case it launches FMPA 16.
It doesn't matter if either FM version is already open, the file opens in the older version.
This was reported by me in the thread for the preview version but has not been fixed in the release.
Workaround (if any)
Drag the file to the FM17 icon or open from the app itself.