Several issues

[bigstiffy]

The "easy crafting bench" causes server crashes consistently when attempting to craft items, I recommend removing it entirely.
The wireless lever from RandomThings will occasionally cause a crash after a player has left the chunk the lever is located, recipe should be disabled.
SpecialMobs with the "hungry" modifier cause server crashes, thief skeletons seem to never despawn,
and headcrumb mobs gradually max out the server limit on mobs because they are typically holding an item and not despawning.
Optifine breaks rendering on tile entities that use layered textures, like item barrels and TiCon tanks, causing the layers to constantly flicker and overlap, sometimes causing items in a player's inventory to flicker until the offending tile entity is removed. Optifine also seems to break rendering of chisel block textures that aren't animated, leaving them invisible and giving a world x-ray view when adjacent to non-invisible blocks. I personally had issues with optifine crashing my client after trying to change configs, I had to remove it at that point.
There was one instance where I ran into a corrupt chunk that may have been caused by archimedes ships, and getting close enough for the chunk to load caused immediate server lock, the only remedy was deleting the chunk so it could be re-generated. No error could be obtained by this, as the server never actually crashed, but rather froze.