I finally found a solution:
While this refers to Adobe products with that same problem, it worked perfectly for me. Even all the fonts etc. are the correct size.
Thank you so much for this!! been driving me crazy and so hard to find anyone having the same problem.
Can't believe we've missed this post for so long. I'm forwarding this thread and the Article posted by vavo to the report with Testing and Development. If we find more information, I will also post back here.
Another endorsement for the fix at Neo Shamon (www.neoshamon.com): Adobe App Scaling on High DPI Displays (FIX)
I have an Asus ROG laptop with 4K screen running 64 bit Windows 10, and was having major dramas with Filemaker (small fonts in value list drop downs, white patches on the display etc), but that work-around got it running again.