I think it might be these mental and physical stative verbs (e.g. know, think, expect, love, live, etc.) that cause the problem.
Partly, yes. Another complicating factor related to your original context is the fact that person B is uttering a
surprised reaction. In such a situation, you wouldn't need to 'explain' anything, just react. You wouldn't typically use the present perfect in a reaction of this kind.
What I have come up with is that these stative verbs are treated as durative. When using them with the perfect aspect, in such cases as provided in the examples above, there appears an ambiguity (for me personally) which is - if the state described by the verb lasted for a period of time in the past and that is somehow influential on the present or the state extends to the current moment of speaking.
I don't follow what you mean. Which stative verbs exactly are treated as durative?
When using the present perfect it actually means that he still lives in Chicago.
That's not strictly true. It doesn't actually 'mean' that, though that would be a likely interpretation. In other words, his still living in Chicago would be
a good reason to relate the past to the present and thus choose the present perfect. But Finn could have reason to use the present perfect even if he no longer lives there.
But in the example from post #25, the relevance is also shown by the past simple.
No. That's not what we mean by 'present relevance'.
In post #17, the 'breaking leg' example shows that both tenses are possible with no difference in meaning.
No, there is a difference in meaning, which is the difference in aspect.
Then I think sometimes the past simple and the present perfect can be used interchangeably
They're never fully interchangeable, because the present perfect always carries an aspect that the past simple doesn't carry.
and with some verbs, there is a difference in meaning as it is stated in post #27. Am I right?
I'm not entirely sure what you mean, but I don't think so, no.
Can we please stick to just one specific context at a time, otherwise things are going to get too complicated to answer usefully.