Note, this has been posted on the Feed The Beast Modpacks Issue tracker, seeing how this is an Industrial Foregoing and Functional Storage issue, this should be easily fixed i assume.
Link: FTBTeam/FTB-Modpack-Issues#1196

Modpack

FTB Direwolf20 1.18

Modpack version

1.8.0

Log Files

Nothing relevant in either latest/debug.

Describe the bug

Some Industrial Foregoing machines appear to stop pushing their output to Functional Storage drawers directly above after a stack or so (depending on the machines output), leaving the remainder in its internal inventory.

Note: I've seen the Latex Processing Unit void items when its internal inventory fills up on a non-test server world. Alas, so far I've been unable to reproduce that aspect in a clean singleplayer world.

Putting a pipe (Mekanism logistical transporter in this case) between the machine and the drawer works around the bug.

Steps to reproduce

1. Place a drawer directly above a powered resourceful furnace set to push its output upward
2. Dump 3 stacks of logs into said furnace
3. Wait for 66/192 charcoal to be output to the drawer

Expected behaviour

Entire output of 192 charcoal gets pushed to drawer

Screenshots

Latex Processing Unit:

Resourceful Furnace:

Workaround:

Additional information

I first noticed this with the Latex Processing Unit but the Resourceful Furnace (picked at random) also exhibits similar behaviour.