The Three-Part Pattern Became a Two-Part Pattern

 Photo date: November 13, 2020. Photographer: Mark Mahin.   

I took the photos below while photographing only ordinary drops of pure, clean water falling in front of a black featureless background.  On this day I got the three-part pattern shown below:

The pattern then lost its feature on the left edge, and became a two-part pattern that persisted for almost all of thousands of consecutive photos.