Phase margin measured at lowest positive-gain point, rather than 0dB point?
Phase margin is defined at the zero dB crossing of the gain.  A system that has a phase dip that touches -180 degrees with positive gain will still be stable if the phase margin as measured where the gain crosses 0 dB is sufficient.

This is called "conditional stability" because if the gain changes so that the zero crossing occurs where the phase is close to -180 then the system can be unstable.

This can be problematic because the gain may go through an unstable point during power up, or over temperature or component variation, etc.

That's why it's desirable to have good gain margin as well.  No matter how intuitive it seems, phase margin is NOT measured at the lowest phase dip where there is gain > 0dB, and a phase dip with gain >0dB doesn't predict system stability.

See the "conditional stability" section in this paper.