Can anyone help offer insight into my puzzle performance?

I am seeing the following strange (to me) pattern in my long-term (60 days) puzzle ratings and I don't really know what to make of it.  My game ratings do not look like this, of course sometimes I dip, sometimes I plateau, sometimes I increase, but it is not in this kind of steady wave pattern.  What could be the reason why I seem to consistently go on these runs of gaining rating fast only to plunge again?  Looking back I can find no time period where I just cruised along at an even rating, it seems to oscillate wildly all the time.

I guess my question is, beyond curiosity, am I doing something wrong with puzzles?  I don't feel like they help me as much when they are always either seemingly impossible (those stretches where I plunge) or else ridiculously easy (where I shoot up).  Has anyone found a good way to just do puzzles that are challenging but doable?  For example, it is for me super rare to partially solve a puzzle, like 2/4 steps.  Basically I always either pass 100% or fail with 0%.  Is this normal?