I don't own an escooter so my only point of reference is an ebike.
Could be either the weather is too cold for the batteries to provide full power, or possibly too hot for the motor control electronics to keep cool... looking at the battery cycles being so low (just 81) and how popular Xiaomi scooters are, I think chances are low that the battery is severely degraded
Does the app auto-refresh those stats in real time when you're riding the scooter? Might be worth screen-recording that page while you ride up the hill and then looking at the recording afterwards to see if the battery is being strained, or if the limit is being imposed elsewhere (internal controller etc)
Could also be that maybe you're carrying more on the scooter (shopping/additional person/wearing heavier clothing)? An additional person on the scooter could strain the battery if done frequently, especially if the BMS can't keep up with balancing the cells after the fact during charging