How are you searching for them in your inventory? Have you tried clicking on the party inventory and using the free text search function?
I’ve certainly had difficulty finding stuff before but that has always worked, and once found I can drag the item to my main character and find it in their inventory. I suspect for me it’s mainly been user error and I’ve just overlooked the item or been searching the wrong party members’ inventory, but unfortunately I don’t think it’s possible to see who is holding an item when you search the party inventory so I’ve not been able to verify.
