Sense 2 stuck on Fitbit logo and won't set up

[beckyfirestar]

I’m now onto my THIRD Sense 2 in a month

- bought the first from Amazon, attempted to set it up. It got stuck in a reset loop (Fitbit logo comes on for a few seconds, brightness decreases by two notches, split second view of the clock face, then goes black and starts again). This happened no matter what I tried, factory reset, changing clock face (which was really hard to do given the watch will only sync to the app for a split second). Eventually gave up assuming it was faulty and sent it back to Amazon. 
- Got another one through Amazon. Same problem! Contacted Fitbit, who agreed I had done everything possible so it must be a faulty pebble, and asked me to ship just the pebble to them. They sent out a replacement, which I have received today. 
- Third Sense 2. Surely this one will work, right? WRONG. EXACTLY THE SAME ISSUE. And now I can’t even send this back to Amazon as they didn’t replace my rose gold pebble like-for-like, so I’m down £89.99 and have no working tracker. 

With three devices doing the exact same thing, I cannot imagine they’re all faulty. So assume it’s the update. But you can’t seem to set up the device without doing the update!!

Moderator Edit: Clarified subject

[LizzyFitbit]

Welcome to the forums, @beckyfirestar.

I've moved your post to a new thread so we can keep the forums organized. Thanks for the detailed information, and for every step you've tried prior to posting. I'm sorry this is happening to your Sense 2 and so I can look into this, may I know what error message you see on the Fitbit app during the setup process? What's the model and OS version of your phone? Have you made sure to leave your watch charging for at least an hour before setting it up?

I understand you've tried some steps, but please confirm you've exhausted the troubleshooting described in this help article.

[beckyfirestar]

My phone is an iPhone12 running IOS 16.6. The error messages I get related to not being able to sync the watch to my phone, or one telling me to unpair from my Bluetooth and wait for a pairing request, which I never get. The reboot cycle always seems to start after the update is performed on a brand new or factory reset Sense 2, but I can’t see if the update completes and then it goes into the cycle, or if it’s stuck within the update. I suspect it’s after because the software listed on the app goes from .50 to .52. 

Currently, the watch isn’t synced to my phone at all, has been on charge for 24 hours, and is still looping. Can’t even attempt to set it up on my app as it’s not being recognised. 

[EdCarter4]

The update won’t work or let me keep using it at all. Is this forcing me to get a google account? The note I read said I had 2 years. 2025! Why is this update ruining my Fitbit?