I found an odd tool-tip with an "undefined" text, not sure why this happens. This is one of the tracks where it occurs: https://musicbrainz.org/recording/ca0e0413-c086-431a-b0ac-8795aca5aa30. It also happens when editing recordings from this release: https://musicbrainz.org/release/2260aedd-155d-33b0-a4bb-6db7ce3f6598 (again, only via their recording pages). So it seems that this bug only happens when editing recordings from the recording page.
Edited the description to make it more clear. Also it looks like it happens on other places as well, see the post below.