Hi and welcome to the forum with you first post.

As the default album art is typically 200*200 I've updated many many albums with artwork ranging from 600*600 which I consider minimum spec right up to 2000*2000 possible higher in one or two cases.

I've not seen any artefacts like you describe, If you can capture it on a photo do post it.

Regards,
Carl

861v6+ID40, HD621, 8000.2, 7200HC, 7200.2, SKYQ Silver, PS3, PDP-LX6090, QNAP TS870-Pro (8*6TB), Roon, iPadAir2.
[In Reserve] C15, MD600 (2*3TB), TwinStore RM (2*2TB)