I'm sure there are other reasons for having low potassium.I remember when grandma was on diuretics for many years and had to take a huge timed release potassium pill. Tended to give her a nasty bellyache. They never said anything about mag or b12 deficiency.
But B12 shots are known to cause low potassium. And potassium has never in my life been an issue before I started injecting B12 about 6 weeks ago. Neither has my blood pressure.
B12 uses potassium in the healing process. So potassium gets low.