Trying to reproduce the same bandcamp issue locally merged it with the right credit... not sure what's going on.

Thanks for the clarification. Now that it’s clear how merges should be affecting relationship credits, it seems like there is a problem, I’ve only noticed it with labels though:
A recent case Edit #58681499 - Merge labels should have created a relationship credit for the URL relationship added in Edit #24842952, but didn’t.

That sounds correct. It's intended for now in that labels/places/etc. don't have a checkbox on the merge page to "rename" the credits (i.e. keep them empty, thus have them take on the new entity name) like artists do. I think we should add that checkbox to all merge pages, but since it's not there yet, I guess preserving the old name in the credits was the safer/more conservative option.

Using test.musicbrainz.org, if I merge label FOO into label BAR, this is the behavior I’m seeing:

• Any relationship credits that were entered manually on FOO are kept after the merge.
• Any relationships on FOO that did not have a relationship credit entered, will have a credit “FOO” added as part of the merge process. So after the merge, these relationships read as BAR (credited as FOO).

I’m getting the same thing happening when merging places. Is this the intended behavior?

I think the credits are kept when they have been specified by hand, but if they just use the default entity name without an actual entered credit then that relationship will change and use the new default entity name when the merge goes through. Same difference about whether they get renamed on renaming the artist (MBS-8441).

I think relationship credits are being created correctly in Place merges. See this recently merged Place. However, I’m not sure they are being created in Label merges. It would be good if someone could check this.