I think I found it - when I was creating the layer I was getting an error about the layer already existing, even though it didn’t.
I looked at the server log and it seemed to be Ice.Lib.MetaFX.SaveApp.SaveAppFixNotNeeded method directive.
I’m not sure what created this, but there were two instances of the directive, so I disabled one of them, but it definitely looks like Epicor code (maybe either Document Sender or the Menu Tracker)