You can duplicate your items by pressing many items in your inventory and moving them around your inventory.

See video for example: https://streamable.com/d6aimn

Minecraft 1.15.2

Item is still there after logging out. I can also still use it.

Can you share your items.yml configuration?

allWorlds:
default:
MIN: 32
MAX: -1
player: {}
group:
testGroup:
MIN: -1
MAX: -1
inventory:
chest:
MIN: -1
MAX: -1
testWorld:
default:
MIN: -1
MAX: -1

I've tested this for a while, but I am unable to replicate it. Are you able to replicate this with only StackableItems?

It only happens when StackableItems is ON

Do you have any other plugins running? Can you test this with StackableItems being the only plugin?

Already tested with the previous test

What server software and version are you using?
What OS are you using?
Are you testing this on a local server or hosted?
Are you using a custom client?
If you're using spigot or paper, what does /tps show?

1. Spigot
2. Windows 10 pro
3. Local server (port forwarded)
4. #3rd party client
5. *20. *20. *20. (even right after the bug)

What version of Spigot and what 3rd party client?

Have you tested this on the vanilla client?

spigot-1.15.2 and tested on vanilla but same problem

Can you confirm that these items exist after picking both back up as well as logging out and logging back in?

Just to clarify, which of the three scenarios are causing the duplication for you:

• left click
• right click
• alternating

Also, are you using any tool to click faster?

All 3 scenarios are possible. I tried all 3 of them.

No tools, just my fingers

Can you confirm how you are clicking when you duplicate the items? Are you only left clicking?

Only left button works, same with right and with alternating. It can takes few minutes before succeeding

I click really fast and moving the mouse up and down (also fast)

Tested a bit more with some macro's

It seems it only works when I have

default:
   MIN: 32
   MAX: -1

in items.yml