The gap between the two explosions would correspond roughly to a torpedo's running time. In this case, the main disaster may have been overcompensation and a quick run into the bottom. It is conceivable that, after firing a torpedo, someone overcompensated or the boat suffered a stern plane casualty and began a shallow dive. She is about 154 meters long. Her enormous inertia would make her slow to pull out of a dive.
Shallow water can be quite dangerous for a large submarine.
When the submarine hit, she apparently still was running ahead, since reportedly she dug a furrow in the bottom before coming to rest. Without them, she had no power except for the limited amount provided by a storage battery, plus high-pressure air in tanks. Had the submarine been undamaged, she presumably could have blown her ballast tanks to reach the surface. Many of the reports had her taking up a 60 list on the bottom. That would be explicable if she had indeed tried to blow tanks, but could not get air into those on one side.