Mod List:
Map Atlases 1.21-6.1.3 (map_atlases)
Minecraft 1.21.1 (minecraft)
Moonlight Lib 1.21-2.17.34 (moonlight)
NeoForge 21.1.133 (neoforge)
When I place pins on the map, they disappear after I leave and rejoin the world. However, banners remain as expected.
Steps to reproduce:
1.Place a pin on the map.
2.Leave the world.
3.Rejoin the world.
4.The pin is gone, but banners remain.
Hope this helps. Thanks!

Mind hd king if it works on fabric or 1.20?

It works on Forge 1.20.1, but it doesn't work on Fabric 1.21.1

Issue still happens on both Forge 1.20.1 and Fabric version
Looks to be an issue with the nbt file getting corrupted

I'm having this issue as well for map_atlases-1.20-6.0.17 on Forge. They remove after maybe every 2 or 3 boot-ups. You should consider reopening this.

Replicating this will be a pain. Others have claimed it works on forge so if it doesn't sometimes it must be very rare and context dependent