Reproduction: be on MP server (doesn't seem to happen in SP), place a slimey generator, put milk in the milk slot without putting slimeballs in, watch the server freeze.
I can replicate a very similar issue by attempting to place a milk bucket into the machine with no empty slot, and it completely freezes the client (but not the server). Image attached.
Reproduction: be on MP server (doesn't seem to happen in SP), place a slimey generator, put milk in the milk slot without putting slimeballs in, watch the server freeze.