Where did my Complication go?

I have an app on my iPhone SE that is a time clock so I can "punch in" when I start work and "punch out" when I leave. It was available as a complication of my Modular watch face and I just used it yesterday. I charged my iPhone and Watch overnight, but did not turn either one off as far as I can remember. Today it is not on the watch face and is not listed as an available complication (it is still available as an app in my iPhone and on my Watch). So what happened? How does an app get to be a complication? I did not update my iPhone or Apple Watch 2 yesterday, so where did it go? This was one of my most used complications 😟.