since he has lived in London

[riverkid]

The situation demands context again. If he still lives in London, it's absolutely alright to use the Present Perfect Simple in the since-clause; the situation changes significantly if we use the Past Simple tense:

He has made a lot of friends since he has lived in London. (still in London)
= Between the time of his moving to London and the time up to now he has made a lot of friends.

He has made a lot of friends since he lived in London. (not in London any more)
= Between the time of his leaving London and the time up to now he has made a lot of friends.

I agree with you, Engee. Maybe that's why a native speaker would refrain from using the verb 'live' for this situation. When we use 'move', it makes no difference whether we use the present perfect or the past simple.

He has made a lot of friends since he has moved to London.

He has made a lot of friends since he moved to London.

The grammatically possible isn't always semantically possible or semantically a good choice.

[engee30]

...
The grammatically possible isn't always semantically possible or semantically a good choice.
...

Oh yes, after having read your comment above, I must admit I couldn't agree more on that! To me, as a non-native English speaker, sometimes it is somewhat easier to accept something that wouldn't be the initial choice made by a native speaker of English.

[joham]

I'm a lot clearer now. Many thanks.