Hey mate. Have you updated your device recently? It seems people are reporting this to be the case with the widget on the recent update for (2) (2a) and (2a) Plus. I’d suggest (but can’t confirm) that this is a bug.
On my Phone (1) which hasn’t been updated recently I’m seeing album art for YT music, as well as playback controls (play/pause). I’d suggest either raising this with support or, via Settings > System > Feedback.