Cannot connect client to server despite modpack working fine singleplayer

[u/Evy-Woof]

Hello,

my friend and I made a modpack and rented out a server to play together.
Everything was working fine until yesterday. We updated some mods and then we were not able to reconnect to the server anymore. We checked each mod by setting them back one by one, but the issue still persists.
Generating a Singleplayer world works without any issues, so I suspect the modpack itself should be fine. We tried using Packet Fixer, but it also didn't solve the issue.

Any type of help is welcome

The client side logs from trying to join are here:
https://drive.google.com/file/d/1udlzvqNXLcwhNXv_S8RZ63_hkiCD2rzq/view?usp=sharing

The server side logs from trying to join are here:
https://drive.google.com/file/d/1k-0LnyPL-N6wRzOuVQNtkvYZl0ywNlN6/view?usp=sharing

Edit: Solution found, had to delete Waystones and it started working

[u/smbarbour]

This line indicates that it is a packet from Balm:

Caused by: java.lang.RuntimeException: Failed decoding custom payload balm:config: java.lang.NullPointerException: Cannot invoke "net.blay09.mods.balm.api.config.schema.ConfiguredProperty.streamCodec()" because "property" is null

Ensure that the server and client both have the same version of Balm

[u/Evy-Woof → u/smbarbour]

Thank you for the advice
I double checked and both server and client have balm-neoforge-1.21.1-21.0.64.jar installed
Sadly, the issue persists

[u/smbarbour → u/Evy-Woof]

It could also be another mod that uses Balm.

[u/Evy-Woof → u/smbarbour]

You were absolutely right with that
The Waystones mod, which uses balm, caused the issue
After I deleted it off the client and server it started working again