These crashes occurred either during chunk load or exploration (same thing probably). My players didn't report it, so I don't know for sure what happened. I am the modpack author (One Elf Squared).

It appears to be a mod compatibility issue with Farseek and Streams by delvr. The full report is at delvr/Farseek#27

This issue doesn't appear to be related to BoP, all we are doing is calling an event which is entirely normal (and we're far down the call stack too)

thanks for the information. :)