I found this when I was testing the Series relationship role ‘inspired’. I added the relationship via the Edition editor page and then saved it and everything worked perfectly.

I then tried to edit the relationship via the Edition editor page by modifying it to ‘is part of’ and each time I clicked on that option I got an almost blank page which would not resolve.

https://community.metabrainz.org/t/bug-when-modifying-series-relationship-in-edition/581727