Crash/Disconnect in Multiplayer when swapping items, switching items, or using any of the built in Inventory abilities.
This crash often accompanies the error in your log.
This is caused by failure to init the Gameplay Ability System Globals. You need to call
UAbilitySystemGlobals::InitGlobalData() The Arc Inventory Example Project contains a useful Engine Subsystem for this. You can grab the Engine Subsystem from a github gist as well.
You can find out more information in the community GAS documentation about Initing the Ability System.
Are there any Debug overlays or tools to help see the internal state of the inventory?
There are! Simply use the console command
ShowDebug Inventory to view the internal state of the inventory. This will display a list of all item slots for you.
If you want to see all of the items, set
ArcInventory.DebugDetailedItemInfo 1 in the console. This will show detailed slot info and any detailed debug information for the item that is in that slot. It's disabled by default (as the text can get very cluttered).