I suspect it's because of the "Delay processing resource packs/external configurations until later in the startup process." change, because from version 0.3.1, when joining a server that has a custom resource pack, the game freezes with a "Reconfiguring" text, accompanied by an endless spam of this error message, until I "End Task" Java:

[13:14:09] [Render thread/ERROR]: Error executing task on Client
net.minecraft.class_148: Main thread packet handler
at net.minecraft.class_2600.method_11072(class_2600.java:33) ~[client-intermediary.jar:?]
at net.minecraft.class_1255.method_18859(class_1255.java:156) ~[client-intermediary.jar:?]
at net.minecraft.class_4093.method_18859(class_4093.java:23) ~[client-intermediary.jar:?]
at net.minecraft.class_1255.method_16075(class_1255.java:130) ~[client-intermediary.jar:?]
at net.minecraft.class_1255.method_5383(class_1255.java:115) ~[client-intermediary.jar:?]
at net.minecraft.class_310.method_1523(class_310.java:1283) ~[client-intermediary.jar:?]
at net.minecraft.class_310.method_1514(class_310.java:888) ~[client-intermediary.jar:?]
at net.minecraft.client.main.Main.main(Main.java:265) ~[minecraft-1.20.4-client.jar:?]
at net.fabricmc.loader.impl.game.minecraft.MinecraftGameProvider.launch(MinecraftGameProvider.java:470) ~[fabric-loader-0.15.5.jar:?]
at net.fabricmc.loader.impl.launch.knot.Knot.launch(Knot.java:74) ~[fabric-loader-0.15.5.jar:?]
at net.fabricmc.loader.impl.launch.knot.KnotClient.main(KnotClient.java:23) ~[fabric-loader-0.15.5.jar:?]
at org.prismlauncher.launcher.impl.StandardLauncher.launch(StandardLauncher.java:87) ~[NewLaunch.jar:?]
at org.prismlauncher.EntryPoint.listen(EntryPoint.java:130) ~[NewLaunch.jar:?]
at org.prismlauncher.EntryPoint.main(EntryPoint.java:70) ~[NewLaunch.jar:?]
Caused by: java.lang.NullPointerException: Cannot invoke "net.minecraft.class_638.method_8428()" because "this.field_3699" is null
at net.minecraft.class_634.method_11099(class_634.java:1989) ~[client-intermediary.jar:?]
at net.minecraft.class_5900.method_34173(class_5900.java:129) ~[client-intermediary.jar:?]
at net.minecraft.class_5900.method_11054(class_5900.java:14) ~[client-intermediary.jar:?]
at net.minecraft.class_2600.method_11072(class_2600.java:24) ~[client-intermediary.jar:?]
... 13 more

Pushed update 0.3.3 to CurseForge and Modrinth.

The delay resource load is waiting for the resource pack reload event, nothing spectacular. What modpack, and did you update any other mods recently? "this.field_3699" appears to be the client packet listener instance, and I don't see dsurround in the trace. Do you have a complete log you can link?

I can send a full log later, but can confirm that the only change I do is change from 0.3.0 to 0.3.1 and then the issue appears.
In the meantime, you can replicate it by:
Download and use this modpack: https://modrinth.com/modpack/lekkermanclientside
Then update Dynamic Surroundings to 0.3.1 or later.
Then join this server: gommehd.net
Then try entering their City Building area.
The freeze happens as soon as the server tries to switch you to that (because it's a section that prompts and requires a server custom resource pack.)

With 0.3.0, the freeze doesn't happen, of course :).

Took me hours to pin it to the Dynamic Surroundings mod. (Because I first expected it to be related to a resource pack or a rendering mod, not a sound mod.)
Already did the painful journey of testing the mods until this mod was found to be the reason.
That's why I wanted to log the ticket, because it's so unexpected and I wanted to save others the debugging time.

Caused by: java.util.NoSuchElementException: No value present
	at java.util.Optional.orElseThrow(Optional.java:377) ~[?:?]
	at org.orecruncher.dsurround.lib.resources.ClientTagLoader.loadTagData(ClientTagLoader.java:88) ~[DynamicSurroundings-Fabric-1.20.4-0.3.2.jar:?]
	at org.orecruncher.dsurround.lib.resources.ClientTagLoader.getTagData(ClientTagLoader.java:72) ~[DynamicSurroundings-Fabric-1.20.4-0.3.2.jar:?]
	at org.orecruncher.dsurround.lib.resources.ClientTagLoader.getMembers(ClientTagLoader.java:42) ~[DynamicSurroundings-Fabric-1.20.4-0.3.2.jar:?]
	at java.util.Map.computeIfAbsent(Map.java:1054) ~[?:?]

It's trying to find a registry associated with a tag and it cannot be found. Joy.

Do you know what changed in the modpack recently? I hacked around the immediate issue with tag loading, and it fails further on in a piece of code I have not touched in a while.

EDIT: FWIW I hacked around THAT problem, and I can get it to load.

super nice to hear the feedback!
Is this a hack that i can apply to the pack as well?
Or is this something that can work on a future patch?

Unfortunately, it requires a set of code changes.