The issue

The game crashed after joining an already existing world with AquaAcrobatics-1.11.1 installed.
Logs say that the Somnia mod causes the issue, but the game crash only when the version of Aqua Acrobatics is higher than 1.9.2 or 1.10.0.

Logs

Full log
Crash log

There was a fix to an unrelated issue in 1.11.3, but it's possible it may have been the root cause of your crash here. You might want to give that version a try.

Okay wow, that was quick! Gimme 10 minutes to boot the pack! 😛

Ok, I just tested the 1.11.3 and now the game freezes instead of crashes on joining the world. Here is the log:
latest.log

Does it look like it's related to the new get sprites mixin? (I will test it with just only Jurney Map and others.)

This looks a lot more solvable. What version of JourneyMap are you using? My mixin targets the very last 1.12 version, as I assumed that's what everyone uses nowadays.

I use journeymap-1.12.2-5.5.4 because that is the only version that supports Journey Map Stages.

Okay, I'll add support for the 5.5 series. Here's a quick hack that should disable that mixin for now:

1.11.4.zip

Oh yeah, that was it! Thank you for fixing it and being so active. I appreciate it.
No crashes or freezes in 1.11.4.

Proper support for JourneyMap 5.5 is available in 1.11.6.

I am not able to reproduce this with 1.11.1 by itself or in my private modpack which contains a lot of common mods. As you noted, the crash itself seems to be unrelated to Aqua Acrobatics (perhaps it triggers a bug in another mod?).

If you can narrow this down to a certain combination of mods, it will be easier to troubleshoot.

It seems to be related to Somnia Awoken mod. But until 1.11.1 these mods worked fine together.

I tried running it alongside the Somnia mod (version 1.10.2) and it also runs without crashing, unfortunately.

I assume for you the crash goes away if you remove Somnia?

No problem! I wish I could be of more help, but unfortunately my PC is probably even slower than yours at starting modpacks. There was a potential crash issue in 1.11.0 but it should have been resolved in this version, and it's very strange that there are no Aqua Acrobatics-related errors in the logs.

Hmm, sorry then. I need to investigate it further. I will have time for it tomorrow.
(I didn’t tried removing Somnia, because it takes so much time to boot my pack. I will need to do a binary search).