Fitbit Product Experts Alumni are retired members of the Fitbit Product Expert Program. Learn more
This seems to be a known issue that Fitbit are working on. Keep an eye on the following thread where they are posting updates:
https://community.fitbit.com/t5/Sense/Sense-battery-draining-after-iOS-app-update/td-p/4866910
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Fitbit Product Experts Alumni are retired members of the Fitbit Product Expert Program. Learn more
sorry for my misleading post