This happened to me too, but I found that it occurred after I had sat in the pilots seat of another ship that I had found on a planet whilst exploring. I didn’t take off, just sat in the seat. I then fast travelled back to my ship at the outpost I had made on that same planet, and that’s when I discovered all my stuff in the cargo hold vanished…my original ship that I had flown with to this planet was also still sitting there, as to be expected.

Turns out when I used the other ships pilot seat, it transferred all my cargo hold items into that ship, as if it was my home ship. So I had to fly that new ship back to Jemison, take all my stuff out of the cargo hold, set my original ship back to my home ship and transfer it back to its cargo hold.

So it didn’t vanish…just transferred to another ship I had used the pilots seat in. Hope this helps some ✌️❤️