I changed the maximum stack size in the options to 128.
Al stacks are now called "Item"(stack of128). Nevertheless, coal, ironore and copperore unstack to 50 items, some others i.e. stone to 100, green and red circuits unstack as intended to 128.
I have these mods:
https://i.imgur.com/FaylKUT.png
Edit: I play 0.18.26, but I recognized this issue already a few weeks ago