On the switchcraft server, often 1 charcoal fails to cook 8 logs. The last log seems to have 1 or 2 ticks left before cooking is finished leaving the last log in the top slot.

This is nothing to do with CC or Plethora - I suspect it is a sponge bug.

Duplicate of SquidDev-CC/plethora#86 - it can't be fixed until 1.13.