mobs disappear if I put a name tag on them

I want to report a bug that happened to me when I updated the game to version 1.17 of Minecraft pocket edition, the bug what it did is that all the mobs that I had put a label on disappear after a while when I move away from where they are and not the mobs could have died because he had them locked in an area where they could not spawn hostile mobs.
note: if the text is misunderstood or has errors, it is because the translation was taken from the internet, thanks for understanding