I didn’t see anything that jumped out at me (but I’m no expert) . . . .
One thought: subscribe to sunrise and sunset instead of sunriseTime and sunsetTime. According to @matthewnohr on this thread, a sunriseTime event won’t be posted if tomorrow’s is the same time as today’s (rounded to the nearest minute, I assume). This could explain a failure on a particular day but not every day. Also, you don’t need the payload that sunriseTime and sunsetTime bring.