The Jargon File (version 4.4.7, 29 Dec 2003):

sunspots
 n.

    1. Notional cause of an odd error. ?Why did the program suddenly turn the
    screen blue?? ?Sunspots, I guess.?

    2. Also the cause of bit rot ? from the myth that sunspots will increase
    cosmic rays, which can flip single bits in memory. See also phase of the
    moon.


The Free On-line Dictionary of Computing (30 December 2018):

sunspots

   1. Notional cause of an odd error.  "Why did the program
   suddenly turn the screen blue?"  "Sunspots, I guess."

   2. Also the cause of bit rot - from the myth that sunspots
   will increase cosmic rays, which can flip single bits in
   memory.  See also phase of the moon.

   [Jargon File]