What is the issue?
PDF/UA > Basic requirements > Content > Artifacts and tagged content > Tagged content present inside an Artifact
What does it mean?
There is a marked content container with a MCID that is nested inside an artifact.
How to fix it?
There is no standard method. You need an exact dignosis.
If the related element is marked content, that is not referenced by the logical structure, you can remove the empty marked content container. You have to move the content out of the container before.