In the past, I have enabled 24hr heart rate tracking (originally using this method: https://forum.mobvoi.com/viewtopic.php? ... lse#p14875).
However now I find that no heart rate data collected by the watch (other than forced check of heart rate in the Google Fit app) will sync to Google Fit. I noticed many others seem to have the same issue: https://forum.mobvoi.com/viewtopic.php?t=53836
All steps suggested by Sabretooth in that thread have been followed (as well as a full factory reset then updates) with no luck.
Data syncs from the watch to the Mobvoi app on the phone fine, so the issue seems to be with data from Mobvoi account syncing across to Google Fit account.