I had the same issue when upgrading to 1.15. The app I upgraded originally was built with Phoenix 1.4 and the generator at that time included metadata options in the logger configuration with :request_id, and it had carried through every upgrade until this one.
It was especially nefarious, as it was a hard Erlang beam crash that didn’t indicate what exactly had failed other than Logger. I managed to figure it out after looking at phoenixdiff and noticing that option was removed from the generated config in later versions.
As an aside, I never did look into why this option was used in the first place, and removing it didn’t seem to affect anything I did with Phoenix’s request_id in code. I can’t say the same for your additional :span_id and :trace_id atoms as I haven’t seen them used before.