The inductors aren't coupled. I am interested in non coupled inductor sepics because there are few off-the-shelf coupled inductors for sepic, but, as you know, there are huge amounts of off-the-shelf 27uH inductors of the requisite current rating.
It does ring until the RC snubber is added across the cap (simulation is attached of LTspice)
The 'R' of the RC snubber barely dissipates anything at all when the sepic is in steady state.
Interestingly, if the converter is run open loop in the simulation, with the same duty cycle and frequency, there is no ringing even without the snubber.