Ideas
Same is happening to me on XBox Series X. I'm on level 9 of Conservationist career and keep getting raises (I'm now at +16) and my performance just resets to average at the end of my shift. I tried working from home and doing the tasks and then going in the next day but that doesn't help. Happy to try different things if anyone has any suggestions.
What is interesting is that the Sim I am using was a "super Sim" that already finished this career but I'm using a saved version of her from the library in a fresh save from before she reached level 10 of the career, so I thought I'd just finish it off for this save. I think I saved her way back before Horse Ranch came out, so a long time ago!
I should also mention that I don't think the performance goes up unless I click on Careers and make the progress bar visible. I could be wrong about that, but it seems to be at average until I click and then suddenly it starts clicking upwards, if that makes sense.