@BertrandV The Charge 2 is legacy model that was discontinued in 2018. Older models don’t always work as expected. If you can’t make changes, then I don’t think there’s any solution. Sorry.
There is another long thread in this forum where users report that tracked activities (on the device) don't appear on the app.
Laurie | Maryland
Sense 2, Luxe, Aria 2 | iOS | Mac OS
Take a look at the Fitbit help site for further assistance and information.