Leaving aside why you’d want to do that in the face of the Wiim’s squeezelite client which has no such issue, I see similar results for both the Amp Ultra and Ultra using LMS’ Chromecast bridge, even though the WiiM Home app in Android happily shows the artwork and metadata.
Chromecasting from YouTube Music, for example, works ok on both the WiiM screen and app, but I get different results sending from Bubbleupnp over Chromecast where I get the metadata but no artwork on neither the screen nor the WiiM app, but that might be a setting buried deep with Bubbleupnp that I haven’t found.
The issue at first might suggest that there’s an issue with the Chromecast bridge in LMS (the upnpbridge plugin shows no such issue), but the fact that the WiiM app doesn’t have the issue could suggest otherwise and that it’s perhaps a WiiM screen firmware issue.
As usual, it’s best to submit a ticket to WiiM so they can inspect your device and app logs for clues as to the cause.
As an aside, on my iPad app, I face the opposite problem when playing anything from LMS - the Ultra/Amp Ultra screen shows the artwork and metadata as expected, but the iPad WiiM Home app doesn’t. I’ve bug reported this several times.
