I've raised an issue against the FTB modpack I'm running: FTBTeam/FTB-Modpack-Issues#2324

Please see the above issue for more details and a link to the error log. In short, whenever I solve one of the 3 puzzles in the first layer of the pyramid, the server crashes!

Seems to be a duplicate of #14 , which in turn is caused by JoeFoxe/Hexerei-1.18#68