I had similiar complication issues on my Wear OS 3 watch (posted here Tip on new Watch Face Format from WearOS 4 and WFS v1.4.13! - #13 by davidsung).
Sometimes the complication icons go missing and the text is replaced with __placeholder. @r.liechty_SDR reported this but the WFS team couldn’t reproduce it.
I couldn’t reproduce these issues on a Wear OS 4 emulator myself. Probably something broken in those Wear OS 3 Watch Face Format compatibility binaries.