MC version 1.20.1
Forge Version 47.3.0
User(s) who are failing to connect to dedicated server are both using Windows 10

Description of situation:
I have a modpack running on Curseforge launcher, its been running fine for a while, nearly everyone who uses it works flawlessly. I use a invite code to make sure all clients have the same modpack. 2 out of the 7 people using the server keep trying to join end up having a failure to connect during the Encryption process of the joining server handshake. When we investigate the log (which I will provide here.) it mentions:
"Could not find value 'formations:template_editor' in registry 'minecraft:item' for @RegistryEntryAcceptor" for those 2 clients. However, a 3rd person had the same similar issue too, but when I had them run the executable of MC as administrator and added the launcher/mc executable to firewall settings, it seemed to fix the 3rd person's connection issue.
However on attempt to do the same fix with the other two, we got no successful entry to the server, it continued persisting.
It may not be an actual issue with this mod itself, (Formations.) But I figured id try to gain some insight from you guys perhaps you know about this from prior discussions or experiences.
I just need help with guidance on where to look for a potential resolution.

crash report:
latest.log

...

Could not find value 'formations:template_editor' in registry 'minecraft:item' for @RegistryEntryAcceptor

That is just a warning and does not affect anything.

I am somewhat confused. You selected the crash template. Is the issue just that some players can't connect or is the game crashing?

If the issue is just that some players can't connect, I don't see how it would be related to Formations.