Playing MCEternal, default modlist, slightly altered the config as one of the modes in it is bugged. Has nothing to do with /dank, only tech mods' crafting recipes AFAIK.

Dank Null Version: 1.12.2-1.7.91
p455w0rds Lib Version: 1.12.2-2.3.161
Forge Version: 14.23.5.2854

Steps To Reproduce:
I frankly have no idea what has caused this bug, but it's been plaguing me every single time I decide to play modded with my friend. I just craft an emerald /dank/null, and it works properly for a bit. After some time, relogs, or some other arbitrary metric it just decides to "work" in a weird way. Items are switched around the storage, the numbers rarely go above 64, empty slots may hold items and vice versa - the only thing that isn't seemingly broken is when the dank/null is in my hand - scrolling and placing works properly.

I've been having this bug for a long time and never found out what is causing it.

Was this tested on Single Player or Server (or Both)?

It has only occured to me on my friend's server across several modpacks.

Update: I can't seem to reproduce this bug in singleplayer.

Was this tested with just Dank Null installed, if not what is the minimal set of mods to cause the issue?

I have only tested this within the given modpack(MC Eternal), but I will try to do it with only /dank, and start by adding optifine.

Here's a video of the bug in question.

https://youtu.be/NsJAJ-azz6Y

I have been having the same issue on my Enigmatica 2 1.79 server.

I get the same issue but with all tiers of /dank/null, playing Enigmatica 2 v1.79 on server.

Mods and Forge version are same as OP's

Here is a short video showing the issue
https://user-images.githubusercontent.com/803875/136048990-9eb71855-44bc-4f98-bf72-cc470b38c6ac.mp4

I have the same issue. Added the mod to my RLCraft server.
While the interface is bugged, the inventory seem to work just fine, at least it does for me.
If you hook the /dank/null up to a Docking Station, you should see an "unbugged" view of the inventory.

I am also having this issue, but it also causes a dupe bug.

This is on Enigmatica 2

Shown here: https://www.youtube.com/watch?v=rULMFbLNQEk

(To anyone reading this issue request, I see that this version (1.12.2-1.7.91) is not the latest, only the latest stable. Update to the latest beta (1.12.2-1.7.101) and see if bugs persist. Take your issue up with your pack maintainer)