Bug Very long freezes on WebGL build with Photon (PUN2) on Unity 2021 LTS

We are having a serious issue on Unity 2021.3.3f1 LTS + Latest PUN2 (Nov 25, 2021) from the asset store. Our main target is WebGL using URP and WebGL 1.0. We recently upgraded our project from Unity 2019.4.16f1, but we are facing long freezes when joining a room (our best guess) on Unity 2021 LTS version. However, everything works correctly on the editor.

To test things out, I created 2 separate brand new URP projects (2019 LTS and 2021 LTS) and on each one only imported the latest PUN2 package (Nov 25, 2021), and then exported WebGL builds for each using the "Pun Basics Tutorial" demo scenes, and the same long freezes on Unity 2021 LTS are showing up, while the 2019 build works as expected. Exact same behaviour as our project.

I have reported this issue on the Photon forums but their answer was "That sounds a lot like an issue in Unity or it's exports. I would check their forums, if this is a known issue."

I have uploaded a video with a side by side comparison between builds. Please note that none of our code is running on these examples, nor present in these fresh projects, only PUN2 straight from the asset store. Left is 2019 LTS, right is 2021 LTS: https://youtu.be/VpNFoqgSmWc

 

Did you ever find a solution for this problem ?
I am seeing the same issue here

 

Can not reproduce with the Pun Basics Tutorial exported by 2021.3.24 and running in Firefox 113.