So user error, sorta. Clicking on that corner expand button does cause a crash, but I realized today that I didn't need to click there, and if I clicked on the build database button it would prompt me for my flightsim location and such. That worked fine, and so far the rest of the program seems to be working fine in Windows 10 too. Those corner buttons in other parts of the menu ribbon work fine too, it is just the Nav Database one that causes a crash.

I'm having problems too with a fresh Windows 10 install. I've tried running Plan-G as administrator and in Windows 7 compat mode, neither made a difference. It's a network PC (not my main flightsim PC), the flight sim is P3D 2.5. When I start Plan-G, as soon as I click on the little corner button to set the paths to P3D so I can build the database, it crashes. I've tried both 3.1.2 and the 3.1.3 beta. If I can provide any other information please let me know.