The latest firmware update has caused a lot of issues and sadly, for the most part Fitbit aren't acknowledging it.
The lost steps however has been accepted as an issue and is going to be fixed today (possibly) - here's the post for it https://community.fitbit.com/t5/Versa-Smartwatches/Versa-is-losing-my-steps/m-p/4303418#M193769
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