Just what the title says - this is the third time today it's happened. At first I thought maybe i was mistaken - but no, I wrote down the items and the number (ie 20 lumber) and when I went throught the portal to the swamp realm to get the bishop - his items had disappeared. THIS is a major bug and needs to be fixed. It literally makes your hireling useless
Same thing happened to me. Filled the companion's inventory with ores and cleared the site of power in Gloriana's Tears. Took the portal and it warped me to the Crossways, then I warped to Respite. All companion behaviors are turned off, and I checked all crafting benches and chests, it's not anywhere. Their gear is all still in their inventory though.
Have you given the companion permission to use any of your storage bins? Mine will often unload her inventory into a bin I have given her access to then I can sort things out after. Also fuel sources she will put items in fires and smelters for sure. These would be the places I would check
Have you checked your fires and smelters and such? Have you turned off "Fuel Structures" in your companion's behaviors?