IIRC, i’ve seen that happen to any machine that has had its output blocked.
When the machine is no longer powered, the stuff stays in the machine.
And yes, a chest as a buffer does the trick but does of course require a hopper or likewise to empty. It is still the best solution to any setup that can output more than one stack per second. Where stack is of course dependant on the stack size of the item. Item pipes moves stacks. So a buffer chest means any overproduction is stacked as much as possible before being sent through the pipes.
Anything that enters a chest (or regular, non queue, hopper) is automatically stacked. Thus instead of sending say 4 items of X in a stack every second you are now sending 64 items of X every second.
In a perfect world, you’d have a single block buffering machine that only emits full stacks.
Which is why i tend to have really big bandwidth pipes close to any machine where i buffer outputs in item barrels.
And i’ve also found Ultimet pipes to be surprisingly cheap for what they are, 16 bandwidth for a regular sized one is all one ever needs really, unless you are going for a main bus for everything going everywhere.
Sure, they are difficult to produce and may seem rather expensive. But the alloy overall is cheaper long term than making lesser bandwidth pipes.
It’s really unfortunate that these limitations exists due to how MC works.
Oh and one more thing. Seeing the compactness of your setup looks like it’s all confined in a single chunk already. But if for whatever reason it is not…
I always build all my setups to they fit neatly into a single chunk. Going vertical is fine, but crossing a chunk boundary has the potential for weirdness and broken setups even if any crossed chunks are loaded at all times.
In fact, i leave a 2 tile gap between any machine part and a chunk border because i’ve noticed that neighboring chunks can still tick when something happens at the chunk border.
Again, MC works horribly in that regard and if i had the energy to i would confine all auto processing into a single, minimal complexity, chunk to save on performance and avoid chunk related madness.