MythicMobs may break after teleporting

Summary Mobs may lose all their MythicMobs properties (skills, drops, etc.) when teleporting Build #3650 on 1.16.5

Steps to reproduce Get this config on

test_tp:
  Type: ZOMBIE
  Health: 1000
  Options:
    PreventSunburn: true
    PreventOtherDrops: true
  Skills:
  - teleport @target ~onTimer:5
  - message{m="I am still a mythicmob!"} @trigger ~onAttack

spawn it, go into survival (preferably with godmode or similar) and wait for a while.

Current behavior After a seemingly random interval (can be between a few seconds to minutes) , the mob breaks and becomes a regular mob. This can break systems which requires the mob to perform certain action to proceed.

Intended correct behavior MythicMobs shouldn't break after teleporting.