In view of the fact that my whole understanding of star and planet formation is under serious review now that i have an alternative model of causation, explaining this is even more fraught with difficulty.
It seems plausible for a hydrogen reservoir to build up internally and then discharge onto the surface producing variable results, yet not likely. We would certainly be startled if it happened to us. Yet it may simply be part of every star's evolution but not common to ever observe. I do not like this explanation but we may be going there.