Endermite Despawning with Nametag

So, me and my friends have been on an Aternos Minecraft server for about a month now, and after spawning endermites multiple times, naming them, and pushing them into a minecart, they despawn at random for what seems like no reason. Idk if this has to do with the plugins i use (skin restorer and sleepy), or if this is a general thing that can be changed in game. Thanks.