I tried loading up the pack for the first time and kept getting the error message
Failure message: Sophisticated Backpacks (sophisticatedbackpacks) has failed to load correctly java.lang.IllegalStateException: Failed to resolve consumer event type: net.p3pp3rf1y.sophisticatedbackpacks.common.CommonProxy$$Lambda$4613/0x0000000000000000@71f289a5

Upon switching from AdoptOpenJDK to Oracle Java 8, the game completed loading to the main menu. This might be worth a mention in the pack description, even if not many people use openjdk.

Hey taiyoko,
previously I was playing the game with the older OpenJDK build 8.0.292.10 with the OpenJ9 VM with out any errors.
So out of curiosity I also updated to the newer OpenJDK build 8.0.3020.8 with the Hotspot VM found on Adoptium (https://adoptium.net/?variant=openjdk8&jvmVariant=hotspot). They seem to distribute the new versions moving on from september onwards. The latest build on AdoptOpenJDK seems to be the build 8.0.3020.8 aswell.
I could start the game without any errors.
Where you using the OpenJDK 8 builds?

Hi taiyoko, One of our private Beta testers was also using AdoptOpenJDK and did not run into that issue. Could you please confirm what version number of AdoptOpenJDK you were using originally so I can possibly take a closer look / provide more info?

So the version I have installed is 8.0.282.8-openJ9. Looks like I can try updating and see if that fixes things.

Updating to 11.0.12.7-openJ9 does work, so it's apparently just the older version didn't for whatever reason.