No worries, it allowed me to learn something about spot metering. I should have used the right words to express myself, it usually works better that way 
I will indeed do the test with a scan in the lab. I also have thanks to a post on the NLP facebook account the suspicion that it could be a problem with the scan, several users of this scan (RPS 10M) seem dissatisfied, including one with a grain problem quite similar in my opinion.
For ISO I know I probably made this mistake once (see photo below, with a clear density problem on the negative) but that’s the only time. The grain problem I’m talking about appears all the time on 5 shoots where I use 2 rolls of film each time
