I've seen Fitbit users report issues with the Fitbit app syncing with Strava. So, this problem seems to me to be related to the Fitbit app, not the Pixel Watch. So far, I haven't seen a workaround or a timeline for a fix in the Fitbit forums. The only suggestion that I've seen was to revoke access to Strava and set up the link again. However, users reported that this didn't work for them.
For now, you can submit the issue using the Feedback option in the Fitbit app:
- Tap on your picture in the upper right of the Today page in the Fitbit app
- Select Feedback in the menu that opens
- Complete the prompts and submit
Although you likely won't receive a reply, the team receive & review the feedback reports.