NeoForge 21.1.194
Tom's Simple Storage Mod 1.21-2.2.2
Create 1.21.1-6.0.6

When hooking up an Inventory Connector to a Create Vault and then looking at the inventory with a Terminal it will show X times the amount of items in the inventory, where X is the number of Vault blocks. So if there is only 1 item in a 2x2 vault the Terminal will show there's 4 items instead. This does not happen when attaching a Terminal directly to the Vault or when using an Inventory Cable Connector.

Actual content

What the Invenytory Connector sees

What the Terminal directly attached sees

What a Terminal connected to an Inventory Connector connected to an Inventory Cable Connector sees

I'm also having this issue

This isn't a bug, more just a hassle. You both need to use the "Inventory Configurator" item included in this mod. It's a sort of wand. Click it on your vault and press the big green plus to specify all the blocks that are part of that vault.

You will need to do this for any vault that is larger than a single block. And I believe you even need to do it for any mod inventory that's more than a single block (i.e. a double diamond chest in Extended Storage.)

I feel like this should have built-in support in the mod, a lot of people will experience this and it's not at all obvious that there is such a thing as a multiblock that needs to be configured, or even how to configure it.

I'm considering adding a special case in the Create Contraption Terminals mod. (My Create + Tom's Storage compat mod) But in the mean time you can use the configurator for this.