I had updated my MacBook Pro to the latest MacOS version Sierra 10.12.4. I did not realize that FileMaker Pro 14 was not supporting that version of Apple's OS. After reading more about the support for FileMaker Pro 14 and MacOS Sierra, my conclusion was that it would probably be okay and so I continued developing with that environment. After some time I was working on a layout when all of a sudden I went back to Browse Mode from Layout Mode and the layout was all messed up. Objects were not staying the correct size, and so I assumed my last actions corrupted the file. I pulled a backup and replicated the issue, which it has something to do with copying and pasting. Needless to say, I learned my lesson, I can't be confident that this is due to the unsupported OS, but it seemed to fit.
I have now decided to upgrade my SSD for more space and to partition the drive so I can install an older version of OS X. I looked at the FileMaker 14 technical specifications, and it shows that it will support OS X Mavericks, Yosemite, and El Capitan. My question to all of you is what version is the most stable? I assume that it would be the latest version, but again there might be bugs that the latest OS FileMaker 14 supports has that might not have gotten solved, and FileMaker just moved on to FileMaker 15. If anyone has a good idea of what would be the best OS to use with FileMaker 14, it would be very much appreciated.