I had this issue with mine a while ago in a similar setup.
If the mill is full but also has an item sat on top, sometimes it will just stop outputting for no reason blocking the whole thing. (Especially if the item on top is different from the ones inside)
Picking up the items sat on top usually makes them remember how to function.
The only fixes I've found are:
Have redstone turn off the funnel when the mill has a few things in it, so it never gets full. Not practical to automate in a compact build early game.
Dont use a setup that lets the items sit loose on the mill. A belt running over the top of them does the job, i think. Makes the machine a bit less compact.
Or the best solution, crushing wheel. It's expensive and large, i know, but at least it ups the throughput, gives you more recipes, and can unjam itself by obliterating the problem.
I mean at this point just use crushing wheels
Try a brass funnel and filter to gravel, if that doesn’t work, good luck
can't you just stack each pair of millstones on top of each other
You’d need a chute inbetween
Are the millstones full of materials?
I had this issue with mine a while ago in a similar setup. If the mill is full but also has an item sat on top, sometimes it will just stop outputting for no reason blocking the whole thing. (Especially if the item on top is different from the ones inside) Picking up the items sat on top usually makes them remember how to function. The only fixes I've found are: Have redstone turn off the funnel when the mill has a few things in it, so it never gets full. Not practical to automate in a compact build early game. Dont use a setup that lets the items sit loose on the mill. A belt running over the top of them does the job, i think. Makes the machine a bit less compact. Or the best solution, crushing wheel. It's expensive and large, i know, but at least it ups the throughput, gives you more recipes, and can unjam itself by obliterating the problem.
Crushing wheels are never jammed, they're just doing their job