It'll work for maybe a minute, filling with ores I get from the steam quarry, filled using the inventory hoppers. Then it just stops completely, and only starts after I manually remove the ores from its item input hatch. I can also force it to start again by breaking and replacing the item input hatch.

Something else strange that happens is that if I'm processing ore (not "raw" or "crushed dust" items), the item input hatch only fills up to around 4-6 items and then stops.

I've found I can work around this by having an inventory hopper input into an intermediate buffer chest first, and then item piping the ores in.

This workaround for whatever reason, seems to briefly "fix" the multiblock halting, but after working for a bit longer than usual, I come back to an item input hatch once again showing just a couple ores and a halted machine.

I figured out what it was, classic user error. There was an item transfer speed bottleneck on the output which caused the machine to clog and halt.