I’ll double check, but reproduction steps should be:
- Find a theme with some file that’s not allowed by default (or delete everything from the theme allowed extensions list or similar)
- Try to import the theme
- See it fail because of the extension
- Allow relevant extensions (or just
*) - Still try and fail to import the theme.
The theme might also need some theme components attached to it, I’m not sure.
I originally caused this using my own theme, but AFAIK most themes should be theoretically able to cause this.
Edit:
Right, the only real mandatory condition here seems to be the blocked file, so a theme with a custom font, logo, etc can trigger it if you disallow that file extension. (Also, staff uploads apparently override theme uploads, so make sure it’s not allowed in either setting)