The bug

When you try to /summon a mob in a chunk that is currently not loaded, the command fails. This is a bug for two reasons:

• Java Edition has no problem doing it
• Summoning the mob in-place and then teleporting it to unloaded chunks works just fine
  • NOTE: this workaround is not acceptable as a permanent solution, because it requires you to summon the mob in a loaded area first, and there are no coordinates that are guaranteed to be loaded (including ticking areas). Additionally, selecting the mob cannot be made perfectly reliable, and teleport has undesirable side effects.

How to reproduce

/summon turtle 100000 5 0

Expected result

Summoned new Turtle

Once teleporting there, you should see it

Actual result

Unable to summon object