NBT root tag reading - since 1.20.2 the protocol nbt has changed and this cause a lot of problems with supporting 1.20.2 and above. It causes a lot of problems with plugins which use packets.

Protocol - https://wiki.vg/Protocol .

Edit: 

It can not be reproduced. It is an internal problem that affects only plugin/mod development, but it is necessary also. If talking more simple, since 1.20.2 root tag of nbt uses 3 bytes, otherwise 1.20.1 and below uses 5 bytes. That change broke all plugins those uses packets with nbt 1.20.1 and below.