Case:

I summoned an allay in multiplayer. Gave it a cake, played the note block. It did give me back a cake, but then when I kept playing the note block, it just disappeared. I could no longer find it, the blue signal out of the note block used for indicating that the allay is listening disappeared.  The allay did not fly away.

Unfortualy i had no photos.

But if it was single player, I would have just lost a nice partner mob.

Cannot be reproduced.