Hi Folks
Thanks for all your replies. Silly me, having reinstalled the app I completely forgot about clicking the google fit button.
Having said that, it really is quite annoying that it stopped working in the first place and so necessitated the uninstall, reinstall process. As a result I've lost all my data and have to start from square one.
Hopefully these issues will be resolved eventually. Apart from that, when it is working I really like it.