Cool, let's have a look.
1a) 2nd order self-oscillating deltasigma.
See attached drawing. The modulator has two poles at DC, one real zero before the intended switching frequency, two real poles after it.
Now look at the phase plot. As close as the phase shift gets to 180 degrees at low frequencies, it never gets there. It has only one crossover point at 180 degrees (here 133kHz). This is expressed as "second order loops are unconditionally stable". After an overload, the loop will always return to stable oscillation at the one and only crossover point.
1b higher order deltasigma modulators.
These modulators /do/ cross 180º at a lower frequency. Therefore, the modulator has two potential oscillation frequencies. However, for stable oscillation to persist, not only must the phase shift be 180º, also the loop gain must be unity. In this case, the "gain" is large signal gain. As you are undoubtedly aware, gain of two-level systems is inversely proportional to the amplitude of the oscillation as seen at the comparator inputs.
When the modulator starts up first, oscillation will start at the intended frequency. Once that is established, and because the attenuation of the two integrators is large at this frequency, loop gain is large. At the lower 180º point, therefore, gain is much higher than 1 and the system will be stable.
Now, when the modulator is overloaded (clipped) large signal gain becomes low, because the amplitude at the comparator is high. The integrators run away and instantly, gain is so low that the lower oscillation frequency becomes viable.
So, deltasigma modulators of order >2 start up stable, but are not unconditionally stable. They can shift to "unwanted" modes after an overload.
The problem is usually addressed by clipping the integrators, thus increasing system gain, preventing stable oscillation at the lower crossover frequencies. In this way, it's quite easy to build high-order systems that come back stably after overloads. I'm doing this as a matter of fact in discrete A/D circuits, where I usually employ 6th or 7th order modulators.