So in versions 1.15.2 and the 1.16 snapshots up til now, I created multiple maps and displayed them on item frames. The map I wanted to see was the map that i was in and the map was last updated in 20w11a, the version before 12a.

UPDATE: the issue was caused by signs. and it just so happened that my map detected a sign block and crashed the game.

What I expected to happen was...:
I wanted to see if my map needed any updating, so i punched it off the item frame and picked it up.  signs are well.. just signs and they are supposed to not crash the game...

What actually happened was...:
After punching the map, picking it up to update it, instead my game froze and it crashed. Logging back in, the game still crashed.

signs crash the game after placing one, unloading the chunks, then loading back the chunks to see the sign (or in my case, having a map detect the sign)

Steps to Reproduce:
1. Make a map in versions before 12a (1.15.2 to 20w11a) (and according to the crash report, it mentions something about a jungle wood sign, so plop one down where the map is too i guess)

2. Update it to 20w12a

3. put it on an item frame unload the chunks by logging off, tp-ing far away and back, etc.

4. Punch the map off an item frame and look at it. reload the chunks with the sign and look at it, or use a map to map it

5. Crash.