I think I discovered the reason why Apple Music Lossless was behaving weirdly on my Eras 300. It would work sporadically, or require the scrubbing trick to get it to play a song, and this happen every single time after an Atmos song would finish playing.
I disabled the Spatial Audio feature from the settings, and now lossless works perfectly! This is still pretty annoying, because the reason I bought the Eras 300 was for the Atmos support. I hope they fix this issue soon.