I have only asked one question at the start of this post - “Please can someone with the same controller confirm if they get similar fluctuations?”
As I said, I have intermittent (and strange/random) poor running (and a dead ESU decoder). I deliberately didn’t list any problem examples, because I didn’t want to muddy the water and take the focus from my question.
Whilst nobody has categorically confirmed my readings are normal, some have suggested that the readings I see are probably ok and I’m inclined to agree, so I’ll close the topic.