Recurring Back Spasms

I have recurring back spasms about once a year. They are debilitating, always happen to the same side of my lower back, muscle relaxers are impotent against them, and it is the Quadratus Lumborum muscle.

It is always left side and I am right handed; I played a shitload of golf the last few years, is it possible I have developed a muscle imbalance? Right now, when it happens the only fix is a deep tissue massage specifically on that muscle for an hour before it finally gives up...super painful and then it's still another week or to slow return to activities (2 weeks until light club swinging).

I have started pilates and running, but curious if anyone else has this same problem and what the root cause is? I'd love to strengthen whatever weakness is causing this to solve the problem for good. Appreciate any recs