My only guess is that the Inventory you use in the UI is not your character.
Is possible you've set the character prefab as the panel owner rather than the character in the scene?
If you spawn the character at runtime you should leave the panel owner field as null and you should be using the PanelOwner ID using a Dynamic Panel Owner component
By default the Inventory Demos are setup such that both the player inventory and the UI are in the scene. But in some cases you . . .
opsive.com
If that's not it then I'm stomped...
You can send us your project using google drive (or similar) via email at support@opsive.com. And we'll have a look in detail
I re-assigned the Panel-owner in the Display Panel Manager but it didn't fixed the issue. However, there is chance that I assigned the prefab rather than the scene instance.. I will scrap whole inventory system and re-establish it and see if this would work. I will come back. Thanks.