On some occasions, you can use a repeated I without who.
A: Who do you love the most?
B: I'm the person (who/m) I love the most.
But this is because the subject and object are the same - I, me.
I love myself the most. I saw myself in the mirror.
(1) Then, suddenly I heard the voice of one of the other members of the research team WHO I´d met earlier.
In this case, there is a potential problem with knowing whether the referent of the relative clause is "one of the members", or "the research team". This would be especially so if instead of 'team', a more personal term like 'the research people' was used. But that's another problem.
So, the rule you quote:
WHO (or WHICH) can be omitted if the verb after the relative pronoun has a DIFFERENT SUBJECT.
does not mean that WHO (or WHICH) cannot be omitted if the subject is the same.