I think I see two threads about the same issue, and I'm not sure which is the "main" thread, but since the other one has a title focused on PS5, I'll add my information here since I've encountered this bug on Steam.
Reproduction Steps: Putting forage/scavangeables into the dehydrator in the evening and checking the machine in the morning. The machine will show as finished, but after removing one dried product, the others will revert to the original state (but with the status bar showing partial drying progress).
I have tested: spending the day before partially underwater; spending the day before entirely on land; using only 1 item type (although mixed qualities); using a combination of item types; putting in items after 1am and sleeping; putting in items between 10pm and 11pm and sleeping; checking the machine immediately in the morning; going into other buildings in the morning before checking the machine; and comparing with setting the forage into the dehydrator 2 hours before a festival and checking the same night in case the time warp would do anything (in this case, it did not).
Repro Rate: seems to be consistently every time I fill the dehydrator before bed and check in the morning. If I ignore the exclamation mark for a few hours of the game-day and instead go to empty the dehydrator in the afternoon, everything will be successfully dried.
Game Platform: Steam, PC
Game Version: v1.2-1239
Input Mode: Keyboard and mouse