There are so many threads here about this scale and the problem we all seem to have in-common, that rather than comment this to each one, I'm starting it as its own thread.
The common problems seem to be the "worked once", or the "can't invite others".
I may have stumbled on a [partial] fix, and wanted to share, in case it helps anyone else with those problems.
We had changed our account profile's "email address" to a different one than the one we originally signed up using.
Invites to use the scale never worked ("something went wrong") and the scale seemed to forget each of us after one weighing.
After changing our profile's email addresses back to the originals, things started working better. I was able to invite my spouse to the scale, and it has logged my weight a few times now, without my having to force close the phone app.
My hypothesis is that different parts of the Fitbit 'system' (all those servers with apps developed over time) key on settings-email, while others key on the original email (using it as a sort of Account ID which would not be a good software practice, since it's supposed to be changeable).
I discovered this when, after being unable to invite my spouse using the settings-email address, I tried inviting her using her original email - not the one she had her account set to use - and the invite was sent instead of me seeing the toast alert that "something went wrong".
