This theory’s been around long enough I watched a program a couple years ago, where they conducted a test replicating the effect of a (relatively low) percentage rise in the proportion of methane into the air intake to an internal combustion aircraft engine.
The effect was immediate. The engine simply stopped.
A prop airplane flying into a methane cloud rising from the ocean, would simply fall like a stone into the sea.
The window of combustibility for methane is pretty narrow for concentrations in air (got that factoid from my gas company). If a bit too rich or too lean, just won’t burn. So could see how it might put out an engine.
Against that seems to stand the failure of insurance companies, who actually get and pay claims and know what has been lost and where, to notice the area as any worse risk than the rest of the ocean. Maybe those ocean fissures are very old, as in centuries if not millennia? And Mother Earth has gotten over her Bermuda burps, at least for now?
A similiar show (or maybe the same one) I saw where they injected a stream of bubbles under a boat and caused it to sink.
Methane hydrate will burn at room temp (fire ice) and will fizzle like an alka-seltzer if it’s disturbed by an earthquake and gets dislodged bringing it closer to the surface. It can cause enough bubbles to sink a boat. I assume as it rises through the atmosphere it could cause engine failure in an aircraft.