Big issues setting up Sense 2 on two different Anndroid Phones

[SwedBear]

I'm slowly wanting to throw this pice of ... away.

Bought the Sense 2 for my mom as her previous Versa watch started dying (working a while then green screen of death). 

We set it up on her Samsung S20. Worked first time. However, she said that she noticed that several of the features was not working and the watch started rebooting during the night. 

I came and we removed it from her fitbit app (and the old one) + factory reset the watch. But now it refuses to connect. The app senses the clock but has big troubles pairing it via the code. Most of the time the code do not even show up.

Thinking it was something with her phone I brought it home to test it. had no issues connecting it to my iPhone and have it set up and working. Factory reset it again and decided to test with my sons Motorola one Action (Android 11).

Same issue. the app finds the Sense 2 right away and then tries to connect. Sometimes I get the code after a few minutes, sometimes not. When I enter the code several times the clock shows a checkmark that I have been connected. But the app claims it still is trying and fails. once the clock decided to spontatinously reboot again and show the lang selection again. 

resetting everything and adding it to my fitbit app in iphone works again.
Seriously .... Google OWNs FitBit and they cannot get a simple pairing working between Android phones and the clock? I have tons of products that have no issues pairing with the phone, including older fitbit products so what is happening?

Do I have a faulty Sense 2?

I've read : https://help.fitbit.com/articles/en_US/Help_article/2322.htm. - nothing there really helps.

Anyone with Samsung S20 /Motorola phones who can give some tip on getting this to work. Otherwise I guess I have to return it. 

[LokeAa]

The account you are using is a Google Account, not a Fitbit Account? All new devices require Google Account.

[SwedBear]

Yes, Google accounts. Like my own my mothers were transfered at some point. My son never has had a Fitbit account so for him I set it up new. The account itself was easy to set up, it is the pairing with the watch from the phones that just won't work well. 

[LokeAa]

I suppose you have tried to toggle off bluetooth on the phone - wait 10 to15 secs and toggle it back on? The only other thing I can think of is to clear bluetooth cache.