Same disc drive: Varying error handling performance?

Hello.
The same disc drive sometimes manages to read the same sectors on a damaged disc, sometimes it does not five minutes later (next ejection).
It is a Pioneer DVR-107 from 2004.

Shouldn’t the reading performance always be the same? Do weather conditions (temperature/air pressure) matter?.

It could also be that the drive is sometimes not receiving sufficient power and therefore the opu can’t focus properly on the disc?

Power supply is always exactly (measured) 12.2 Volts.
0.2V should make no difference.