@Ralf_Karpa Roon provides metadata as a service and metadata changes all the time as a consequence of raw metadata provided to us and changes in our backend processing.
Sometimes genuine improvements to the overall metadata have undesired and unavoidable side effects — Bryan Adams being renamed is one of them (the root cause of which is Bryan Adams’ lawyers instructing removal of his metadata from AMG/Rovi/TiVo’s database) — but this is a rare high profile case, and we will fix it as soon as we can.
With regard to artist images disappearing, this is probably because we merged some artist ID duplicates (which is an improvement), but unfortunately, the ID against which you attached the image no longer exists in your library.
I apologize for any inconvenience caused, but we have to make changes for the long-term betterment of the product. We appreciate this kind of feedback and we will endeavour to resolve metadata issues as they arise.