It remains unexplained but things are correlated with it, and possibly have an unexplained causal effect.

There are side effects of monitoring.

"Angelcare voluntarily recalled 600,000 under-mattress sensor pads after two infants died of strangulation when the cord attached to the pad wrapped around their necks" - http://www.slate.com/articles/life/family/2014/02/mimo_and_o...

Strangulation by baby monitor is correlated with having a baby monitor.

No, baby monitors have been studied. It's not a big mystery. Monitoring doesn't make a dent in SIDS. Education does. "Don't put infants to sleep on their stomachs".