Error scanning remote library

Steps to reproduce

1. subscribe to a remote library, either public or private, e.g. the Free Music Archive on open.audio
2. getting confirmation of the owner
3. manually scan the remote library

What happens?

after a few seconds library box shows red colored text indicating the failure of scanning

What is expected?

after subscribing and aproval by the owner of the remote library the local instance should retrieve all the metadata for its own database

Context

Funkwhale version(s) affected: 0.20.1

non-docker, apache as reverse proxy

Output of journalctl -xn -u funkwhale-server https://framabin.org/p/?5bae5435afbdce65#ZTR7Z9g8HaRWTUVZIi9RdKkTFHLSLn4FSX5DDhfVHpM=