Could it perhaps be this line in the MediaMonkey.dll, and how it is being consumed in Rainmeter?

internal bool EnableArtUpdate = false; // Updating albumart can be expensive, only update if needed

Love this... thank you so much for putting this all together and creating the MediaMonkey.dll that works with the MM5 api. Quick question on cover art... I am having some issues with it intermittently disappearing... and wasn't sure if there is something perhaps occuring on the side of the api --> d...