When using item ducts on the inferium furnace. The item ducts send items but the items dont place into the inventory of the furnace at all, essentially acting as a void chest randomly.
Heres a video of whats happening.
https://youtu.be/jo3P4d9vRgU
heres the report link for the cofh guys about it.
https://github.com/CoFH/Feedback/issues/776

Kinda hard to watch a video that doesnt exist

Should be viewable now, I usually don't use the unlisted/private buttons on youtube.
https://youtu.be/jo3P4d9vRgU

I dont think its on you end now it also seems to be happening with vanilla furnaces as well.

Yeah, I kind of figured that, considering my furnaces are just slightly modified vanilla furnaces anyways.

So it seems to be a forge thing according to kinglemming
https://github.com/CoFH/Feedback/issues/779
It only happens with furnaces none of the other machines seem to be affected by it.

Have you tried using a different forge version?

Ive tried it in different versions of minecraft both of which still has the issue with only itemducts as hoppers and other means of moving items dont do it.

Definitely a weird issue. Hopefully you can find a solution, as I can't really think of one.