https://we.tl/t-qIZkMAX20A
this save does have a few different mods in it, shouldn't matter in this case as the root of the problem is as follows:
when machine starts to work the inventory is checked
find all items that can be condensed
determine available slots for overflow between tiers
start the process
in this case the amount of open slots are determined and 86 copper plates epic tier can be condensed where some overflow (16 plates) will go into another slot as overflow
while the machine is condensing new plates are smelted
new plates are put into the machine making the once available slot filled with a different tier that will not allow the overflowing plates to stack
when machine finishes it can't insert all the plates since the slot it had available is no longer open
crash happens because the remaining plates can't be placed anywhere
Idea for possible solutions
First idea (losless):
Add overflow slots which act similar as output only slots like the various crafting machines have
If any items were left over insert them into the overflow slots
When items are in the overflow slots allow them to be picked out by inserters but block the machine from running until the overflow is empty
Second idea (causes loss):
Void any items that would have overflowed allowing the machine to complete
Third idea (could stall the machine forever):
At completion check the items that can be condensed taking available slots into account and perform condensing action at this point rather then calculating the items that can be condensed at the start
This could result in the machine being overloaded with quantities of items that can't be condensed and would permanently stall the machine from being able to condense, could possibly attach a warning event to it and pause the machine from doing anything to let the player deal with it
Fourth idea (not sure if the base game allows this at all):
When the machine runs do not allow new items to be inserted
