Block entity_nbt_num_get is not synced between client and server automatically

https://drive.google.com/file/d/1xTncIvXqdq-c0wKagLBjJCXSsWEyQR-a/view?usp=sharing

It's on a couple different procedures, the simplest of which is pictured here. Best I can tell, it's whenever I set or get custom nbt data from an entity.

Not specifically one, but it's one of a few that are called at once. I know the error they got, at least. If you have more experience reading error messages than I do, then please feel free. I am doing my best with it.

This is the error message:

[16:07:35] [Netty Client IO #1/ERROR]: Network Exception Caught

java.lang.NullPointerException: Cannot invoke "net.minecraft.nbt.CompoundTag.m_128471_(String)" because "nbt" is null

at net.mcreator.owlspocketdimension.network.OwlsPocketDimensionModVariables$PlayerVariables.readNBT(OwlsPocketDimensionModVariables.java:302) ~[OwlsPocketDimension-v1.0.2_Forge-1.20.1.jar%23516!/:?]

at net.mcreator.owlspocketdimension.network.OwlsPocketDimensionModVariables$PlayerVariablesSyncMessage.<init>(OwlsPocketDimensionModVariables.java:325) ~[OwlsPocketDimension-v1.0.2_Forge-1.20.1.jar%23516!/:?]

They said the error occurred whenever they exited and entered my custom dimension. That would use these procedures here (plus the one I already sent):

https://drive.google.com/file/d/1YndWvzceJQYD2t2ODzQ68GG2ikfmVbXS/view?…

https://drive.google.com/file/d/1BEao0MUSS2Xyrm8UFV-fM9OlsEu2umvG/view?…

https://drive.google.com/file/d/1D1cBQZWwOIHLi5oitMeVP8otgsCt-fPl/view?…

Two of those are screenshots of the procedures, the last one is the primary procedure (the screenshots cut off part of the procedure despite how far I zoomed out, it cut off part of a spawn particle block and part of a teleport command).

It's one of these (or the one I sent in my last post), as these are all the procedures called when a player moves to and from the custom dimension, which is when the user said they got kicked from their server.

I can see that the error points to specific lines of code "java:302" and "java:325" but I don't know how to locate which procedures those are with MCreator.

I am mostly shooting in the dark trying to diagnose this error. I suspect it might be the warning on MCreator pointing to the same thing, but I am uncertain. As noted, if you can read this error message better than I can and better point me in the right direction, I would be grateful. I'd like to fix the error in the procedures regarding nbt data not syncing whether or not that is the cause, but I crucially need to fix the error this user encountered, if that is possible.
Either way, whether you can help or not, I appreciate the prompt replies and attention.

I don't have a hosted server or friends to test it at present, so unfortunately no. I've never encountered it before myself, either. They said it didn't happen on single player or when they were alone on the server, so it may have something to do with multiplayer / having more than one person online.

Only custom nbt number tags within procedures. I am using a boolean variable for each player that is player-persistent with an initial state of false, so I don't know how those would be null. But that's all I can think of as being at fault.

I'll do what you suggested and see if I can replicate the crash in the meantime.

I didn't manage to replicate being kicked from the server, but I think I might have found the issue that has led to their being kicked on their end (despite for some reason not being able to log into the server from another client, maybe something to do with running both clients on the same computer--I don't have another one). Or at least it is an issue. On either server or starting an LAN world, player-persistent global variables seem to just fail for some reason and cease functioning, resulting in some weird fall-through issues that do not happen on single-player worlds or any of my other testing.
I guess it's because player-persistent variables are stored on the client side? That might explain why when they re-log or restart their game, the are able to clear the issue. Is there a way to ensure everything is synced on the server side, or should I be investigating another method?
Do entity nbt values persist after player death? I don't know of very many workarounds for this. My mod relies on knowing where the player has been and certain data associated with that.

No, that is helpful. I did not know any of that. Thank you.
I have confirmed that their error resembles my own experience with inconsistent, occasional desync of the server and client reading the player-persistent variables. Reading MCreator documentation, Player-Persistent Variables are primarily client-sided. So I don't know that it's my fault. Technically. But I think I might explore using something like the File Manager plugin to make an external database that can be read server-side (client doesn't need to know most of the information), but I have no experience with anything like that. I guess I could search for tutorials.

Thank you for your help. I appreciate it immensely. If you think of something else I am all ears, but I'm getting the sense that this may not be strictly the fault of my system and more a consequence of an inconsistent server/client miscommunication.