Can confirm, they reappear when you open them

I play on experimental, and i have a similar problem. I had one character, which broke its legs. I left the game, when i rejoined, i had a new character. I thought the first one had died in the meantime, so i didn't wonder.
I played two or three sessions with the second, when at one point, i started with the first again. I killed him by jumping of a cliff, but i only got a new character, i never saw the second one again (except sometimes on the start screen, but never in game)

Happened to me when i playerd on experimantal accelerated time server 0-3. Got kicked and when i rejoined, i got the error.