When items are shot through Nether portals and removed with hopper minecarts, very occasionally this can cause a crash

The world has a chunk loader that shoots items through Nether portals to and from the Nether. When the items arrive in the other dimension, they are removed from the world using hopper minecarts placed below the Nether portal and recirculated using a simple redstone mechanism. Very rarely, this can cause a crash.

A crash report is attached which includes a stack trace.