I know you ran the updater, but I would suggest reinstalling it and upgrading it cleanly just in case there is something wrong with the installation. Unlikely, but a possiblility.
Off hand maybe something like a script step that pushes the window off the viewing area such as the top window being set to -1500 pixels. Tell Windows to tile the windows and see if it comes back?
I have tried reinstalling but didn't help.
Somtimes I can go for months without a problem, and sometimes it happens 2-3 times a day.
Usually happens when I'm editing layouts, don't recall it ever happening when just using the application.
When it happens the FileMaker starts running as a background process and not listed as a running application.
Probably not a lot of help for you, but I've been running FMPA13 on Win8.1 and never had such a thing happen. Can't imagine it would make a difference, but I have the win8.1 start screen disabled and removed or disabled all those 'apps' 8.1 came with.
Same here. I have never experienced this while using FileMaker 13 on Windows 8.1. Granted, I usually only work in that environment once a week. I will keep an eye out for it.