before the update, I could put in 3600 iron ores in a max upgraded furnace with 6x10% productivity modules and I would get 56000 iron plates. ~15.5 times more than I put in. When I put the 10x steel plate option, I'd get 36000 ores to 36000 iron plates, but unable to use productivity modules.
for assembly machine:
3600 copper plates input, 4 productivity modules means 360021.4=10080 copper cables. But in-game, I'm getting 19000 copper cables, that's double of what I should be getting.
I see the setting to change it from the default 4 but that can only be done at the start of the map. But it seems irrelevant... sorry that I can't provide more details but tl;dr productivity modules are pumping out more items than they should.