Yep, completely normal, and we've all been through it.
First, the average resets when you tier up. The score you shot on the round you tiered up establishes your first average, and it will seesaw from that point until you reach saturation, which as a Master is not that many rounds.
Second, alt shot, blitzes and CTTH games do not count toward your average.
Third, one over for nine at St Andrews is 37, which equates to an 18 hole score of 74, so your average is right where it should be.