Problem/Motivation
This is a bit of a complex bug I'm encountering. It involves 3 core modules and optionally 1 contrib (pathauto), but I think content moderation may be at the heart of it because I can't seem to reproduce it with non-moderated entities.
The problem is that a translation of an entity cannot be saved if the path alias differs from the published original language version.
To reproduce:
1) Create a node type.
2) Add a moderation workflow to it.
3) Add another language to your site.
4) Enable content translations on that node.
5) Add a pathauto pattern to the node that contains the title.
6) Create an English version of the node.
7) Publish the node through the workflow.
8) Add a translation of that node. Change the title.
9) Save the node (as a draft or other unpublished state - I'm not sure why you can save it once but not a second time).
10) Edit the node again and try to save again (as a draft or other unpublished state).
Form error: "You can only change the URL alias for the published version of this content."
My initial thought was that Pathauto was to blame but after looking in PathAliasConstraintValidator.php I feel like there needs to be some additional logic for translations, moderation, etc. I think (not know) that Pathauto is just exposing this issue because it's changing the alias.
Proposed resolution
TODO
Remaining tasks
Investigate further.