Hi, today I spent 10 hours in the mine, I caught three blocks, after the reboot they disappeared like this. The screen was not copied. Question. Copy screen After each block?
You most likely hit blocks on a fork.
if you have poor latency, or poor hardware, you will probably have a lot of fork issues.
Another possibility is that he has been mining in a browser with privacy settings set for anonymous navigation. In this case, if I'm right, if you don't save the wallet it will disappear if you close the browser. Just in case, I'd recommend to everybody to backup ASAP your own wallet.