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?
The version of the theory I heard, wasn’t methane from “fissures”, rather that the undersea geography specific to that area within the triangle - deep mounds of shallow water sediment, on steep declines from the continental shelf down to the depths - were in effect perfect for generating the undersea equivalent of an avalanche.
The sediment, due to organic matter in the runoff it’s comprised of, sits perched at the edge of that undersea slope - saturated with methane bubbles. A suspension of sorts.
When one of the periodic “avalances” occurs, it released large amounts of methane all at once. Whatever happens to be sailing, or flying immediately above that spot at the moment it happens.
Will for all intents and purposes - vanish. All hands lost, because the water pressures involved in a ship or plane first dropping through low-density gaseous bubble saturated sea water, which then at some point immediately resumes its full density. Would be catastrophic for any humans who went through that.
IMHO the theory is sound. It’s a good explanation for the mysteries. And probably not just theoretical.
Probably happens. Just like the stories say.