item menu icon is just flat out missing*

Battle Items are being fazed out, meaning that their usability in the game is being decreased dramatically. Personally, I don't know where you can still use items but in their current state, there's no point in purchasing them anymore.

Here's a link to a previous post that mentions items beginning to be removed from the game:
https://forums.socialpointgames.com/topic/12839/items-in-adventure-map-removed

Anyways, I recommend saving your resources by not spending them on items and saving them for other uses. Hope that satisfies your confusion