Investigators have determined that the September incident was likely caused by super-cooled liquid oxygen building up in a "void or buckle" between a pressure vessel's aluminum liner and its carbon overwrap. If the oxygen gets trapped in a buckle, it can create friction that ignites the chemical... and, well, the whole rocket. To make matters worse, the loading temperature of helium was cold enough to create solid oxygen, which increases the odds of it getting stuck and producing friction. The stopgap solution is to change the pressure vessel configuration to allow warmer helium, and to return to a "proven" helium loading setup. In the long run, however, SpaceX is planning to redesign the vessels so that buckles aren't even possible.
The timing of both the launch and the associated fixes is critical for the company. The 2016 explosion not only lost a valuable vehicle and its payload, but shook the trust for both clients and advocates of private space travel. Were Elon Musk and crew moving too quickly? SpaceX needs to show that it learned from its mistakes, and that catastrophic failures won't happen again for a long time, if ever.