I think it has two feedback ,0ne is positive and another is negetive ,Q2 and Q4 is negetive ,PT332 Q4 Q0 is positive,when negetive > positive it is stable
I disagree on your comment:"There is only one feedback, and I think is negative.". I also think it has 2 loops ,one is positive, another is negative. if your RRR0-8 is too small around 1/gm same order. the positive loop may conduct it unstable