Do you have multiple instances of the same complication showing, by any chance? I was just seeing the same thing on my watch, but after fiddling with my complications, I'm no longer seeing it. The only thing that I can think of that substantively changed in the meantime was that when I was seeing it, I did have multiple "Rain" Apple Weather widgets showing, and now I don't. And I would also note that when I was seeing the flicker, I was seeing the little raincloud icon in the rain complication flicker. In fact, I think all of the complications that I saw flicker were first-party, so I'm wondering if the culprit is duplicate complications or some other factor, rather than your own complication.