What happened to the original poster? Did you ever find a solution?
I’ve been having the same issue for months and through multiple WatchOS and iOS updates.
I see the issue whether I use the button or raise to speak.
If I see Siri taking a long time to respond, I know it’s going to fail. If I cancel and try again immediately, it keeps failing.
I have to allow it to fail completely and wait for Siri say “Sorry, can you say that again? My apologies. I couldn’t hear what you said.” Then, if I repeat the command it always works the next time.
Are the watches defective or is it a software issue that only two people in this forum are noticing?