The prevailing explanation appears to be exaggeration of reported events combined with human error in an area with variable and extreme weather/ocean conditions. Essentially the answer is, there is no mystery.
The theory that methane hydrate pockets could have been released sporadically and caused ships to lose buoyancy and sink etc. is a fairly a fake idea.
Although there are methane hydrates that have been mapped on the continental shelf of the southeastern United States (western part of Bermuda Triangle) it is believed that if hydrates have been released in this area it was during or at the end of the last glacial period (which ended ca. 20,000 years ago). During the last glacial episode, sea level was some 120m lower than present and decreased pressure on hydrates could have allowed them to release more easily.
Since the LGM (Last Glacial Maximum) sea level has risen to its current level and it is unlikely large pockets of methane gas have been released in the recent past.
In The Bermuda Triangle Mystery: Solved in 1975, the author, after his research, concluded (from Wikipedia): The number of ships and aircraft reported missing in the area was not significantly greater, proportionally speaking, than in any other part of the ocean. In an area frequented by tropical storms the number of disappearances that did occur were, for the most part, neither disproportionate, unlikely, nor mysterious; Furthermore, Berlitz and other writers would often fail to mention such storms or even represent the disappearance as having happened in calm conditions when meteorological records clearly contradict this.
The numbers themselves had been exaggerated by sloppy research. A boat’s disappearance, for example, would be reported, but its eventual (if belated) return to port may not have been.
Some disappearances had, in fact, never happened. One plane crash was said to have taken place in 1937 off Daytona Beach, Florida, in front of hundreds of witnesses; a check of the local papers revealed nothing. The legend of the Bermuda Triangle is a manufactured mystery perpetuated by writers who either purposely or unknowingly made use of misconceptions, faulty reasoning, and sensationalism.