When giving any mob the glowing effect, the effect does not wear off. It continues to glow indefinitely. The only situation I have found to fix this is by having a villager get converted into a zombie villager or by killing the effected mob. The bug began in 21w13a and has persisted through 21w14a. I have not checked 21w15a yet but according to the patch notes, it has not been fix. Thank you for your time.