It seems that Glyphs 902 names the TTFs in the Temp folder .ttf_ instad of .ttf, which means they are no longer copied to the intended destination (forgot to update that part of the code?).
What’s more, if there are old files named .ttf in the Temp folder then these are copied instead, which can cause confusion that is very hard to track down for the user.
I’m having the same problem with fonts generated from .projects files in 903. But only the ones that aren‘t a position zero on the custom axis. Export works correctly if the instances are all configured in, and exported from, the .glyphs file.
Georg, this is the issue I described in emails on June 9 and June 13.
That is fixed in version 904.
Projects files still don’t export correctly.