This goes back to a discussion we had a few weeks back on how much training is optimal. In the old days (in my case, I mean the early 80s), my old teachers used to say as a rule of thumb, twice a week to maintain your technique, 3 days or more per week to get better. And that was back in the day when classes were 2 hours long.
These days, the classes are shorter, and the curriculum is bigger. In a nutshell, there isn't enough time to practice the entire curriculum every class. So for the once a week person, they might go 2, or even 3 weeks without practicing parts of the curriculum. In this era of commercial MA schools, nobody is going to kick you out for not coming to class as often as you should, but by the same token, you shouldn't be surprised if your progress is slow, or even static for periods of time.