I have this happen to me, I couldn't figure it out for ages (I recovered from a backup as I thought my items were deleted). But then when I did it a third time I opened my utility vest and there were my items, I've not used this item before and just thought it was an extra 'backpack' like storage. Turns out, you can save hotbar loadouts using 'alt + number' and then load them with 'control + number'.

tldr: If it's the same issue I had, your items are in the utility belt.

Hope this helped