Also tested with AutoRegLib-1.3-31.jar and Quark-r1.5-167.jar and JEI by themselves.

The config is enabled and this is in single-player.

can't reproduce. Provide log, please?

latest.log

debug.log

I spawned in a shulker box and then some random items and then while the item was in my cursor I right clicked on the shulker box and it didn't go in.
This is using Forge 14.23.5.2838 if that matters.

No

Odd. I'll need to investigate further. I can't see why this wouldn't work...

Did the item swap positions with the shulker box?

This doesn't work for me either. Right-clicking does nothing at all. Tried shift-right-clicking as well which did nothing. I have it enabled and see tooltip.

AutoRegLib-1.3-32
Quark-r1.6-177
forge-1.12.2-14.23.5.2838

No messages related to it in my logs either. I haven't tried with only Quark and AutoRegLib installed though so in my case maybe it's a compat issue with another mod.

@yrsegal

If this helps, adding items to shulker boxes DOES work, BUT, the Shulker box can not be in the hotbar, it needs to be in the main inventory

as i had the same issue, but then it suddenly worked, and through testing, was due to that above^

Same Issue, even now