Error when killing mythic mobs when having taken a quest to kill other mythics. Also error on Quests plugin load.

[Momshroom]

I'm using Quests 4.0.6-b254 , paper 1.17.1, build 190, and Mythic Mobs 5.0.0-Snapshot, build 3742.

When Quests loads, I get this error:
https://paste.gg/p/Momshroom/55960053142d43a68bd25eaf9ea7db0f

When a player has an active quest to kill one type of mythic mobs, I get this error when they kill any mythic mobs (whether or not that mythic is a quest objective). Players without the quest do not cause the error. The error did not occur in Minecraft 1.16.5, but does in 1.17.1 (paper 190):
https://paste.gg/p/Momshroom/b0b20046c6f341d2ace35f4c25ea2046

Here is the quest I'm using when the error occurs:
https://paste.gg/p/Momshroom/8f41f5e58c3349fda461906c792ccf0c

Thanks for any help you can provide. I'm aware the module doesn't even claim to support 1.17.1, so I'm pushing my luck a bit.