Seawolf is a good design. Unlike quite a lot of other cheap sub kits on the market, it features a sturdy cylindrical pressure hull of sound design, and the general layout is conducive to a reliable boat provided good construction standards are maintained.
But there is no such thing as a 100% reliable machine, and subs are no exception, when something does go wrong, it tends to be more serious than other types of model save for aircraft.
Even with a simple dynamic diving boat like the Seawolf, i can think of at least a dozen things that can fail in such a way that results in your boat staying on the bottom, so bearing that in mind, the best thin to do is sail in waters wher you stand a good chance of recovery no matter what happens. Canals, docks and natural lakes are usually the worst places to sail in, becuase they tend to be very deep, or lack visibility or both.