This can only happen if you are in Fortress: Survival.
If there's a system for exceeding the item limit in the inventory, how about a vault as an inventory extension?
The reason for this question is the following error message: internal exception: java.lang.RuntimeException: Tried to read NBT tag that was too big; tried to allocate: 2097167 bytes where max allowed: 2097152
The message is due to too many items in my inventory, i.e. between 10k and 15K items in the player inventory.
The MineFortresse mod (version 1.8.3) has to be installed on the server in 1.20.