Can’t reproduce it but its happening often.
What version do you have? And could you send me the .otf file?
This happens a lot. Even with files created with Glyphs. Most often happens when the app is already open with an existing Glyphs project.
I’ll send you the file next time it happens. I believe I’m always using the latest version available.
I need to know the actual version number (the three digits like 895 or 922).