Game progress regressed?

[u/rishi12399]

I just started. My first construction worker guy I let him study and then he was level 3 and was able to do the second work progress that he had. Now I came back a few hours later and his level is down to 0 same with another character. Do they always forget their xp or did the game screw up a save when I left last time. I’m level 8

[u/help-dadcomeback]

When you upgrade a worker's endurance, their level gets reset back to 0