All the errors on that page are of just two types:
Person is not a known valid target type for the byArtist property – This seems to be a shortcoming of the schema, which only expects groups, but not individuals.
The property creditedTo is not recognized by Google for an object of type MusicAlbum. – The main point seems to be by Google here, because generally it is allowable. I’m not sure it should be considered an error. (A different issue would then be that the schema.org definition expects an entity, not a string; but whatever.)
Regarding concerns, does it cause problems for you? If it did cause issues for Google, I would expect them to contact MeB, so probably not. Note that the MusicBrainz JSON-LD output was implemented for Google and paid for by them, so they do care about it.