The bug
When moving an ender crystal with pistons, it will disappear when the chunk it was originally in is no longer loaded. It will be visible again after the world has been reloaded.
To reproduce
Set your render distance to 2 (only for easier testing; other render distances work as well, but then reproducing will take longer)
Spawn an end crystal
Move it with pistons for a while (for example with a flying machine)
→ ❌ At some point, the crystal no longer rendersClose the world and open it again
→ ✔ Now the crystal renders from all angles again
Videos
Video of me reproducing the bug: https://youtu.be/rVDuA2FKDzM
Video of @unknown discovering this issue: https://youtu.be/ayE-xC5rgIM
Linked issues
is duplicated by
testing discovered
Attachments
Comments

Confirmed in 1.16-pre2.

Confirmed in 1.16-pre5.
I wasn't able to reproduce this in 1.20.1. I followed the flying machine for 5 minutes and the crystal stayed rendering throughout (render distance of 2 and simulation distance of 5).
[media]
Can you still reproduce this issue yourself?
Closely related to / caused by MC-44654, but as opposed to that ticket, this is possible in survival too!