This may be a flavor of Novelty.
Is this a common phenomenon?
Personally I appreciate people being nice, and especially predictably nice. It does have a lot of value to me each time, even when it's not immediately salient.
My immediate emotional reaction if someone is nice on one occasion when they're much more usually unpleasant is confusion and mistrust. Why are they nice this time, and the opposite all the other times? Obviously I still can't trust them to be generally nice in future, but maybe they're expecting me to do so for some reason. It's much more salient, but also much less valuable.
The converse seems much more true: if someone normally nice does something unpleasant, then it is both much more salient and burns a lot more value than someone normally unpleasant doing the same thing. The immediate consequence might be the same, but now I have to update my mental model to take into account that whatever caused their unpleasant act may happen again. It may even happen more frequently, and I should be prepared for that. If someone normally unpleasant does something unpleasant again, then I have probably already prepared for that and the effects will be lessened.
What is a kind of bias in which nice things done by a person who is for example always lovely, have less value to us than nice things done by someone who is usually unpleasant? The reverse can also be true, of course.
If this is a specific type of bias do you know of quality research papers describing this phenomenon or this particular situation?