I've wasted a lot of time reading this and other forum posts and trying to figure out why I've been manually reassigning my weight measurement from Guest to my account for the last few years. Given the time I've spent I thought I should share some of my notes in case they are helpful to others. These are based on what I have seen, read, and learned in talking to a Fitbit rep today (1 (877) 623-4997 -- the first phone tree had an option (I think it was 2) for Aria, and I got on the phone with a friendly chap in less than a minute and had a pretty good conversation -- this may be the exception as far as responsiveness, but my one attempt suggests they can be reached and be helpful). My experience is with the original gen 1 Aria that came out in 2012. It is important to note that the Aria 2, which apparently features a larger screen, bgn networking, and some ability to tell the scale which user you are is likely a bit of a different beast when it comes to possible resolutions. I should also disclaim that my own scale appears to have a non-working BF% sensor and presumably because of that none of these will work for me.
Another aside: I've noticed that the weight my scale reports and the weight captured in my app are different, usually by .1 or .2 pounds. I would speculate that Fitbit is actually storing weight in kilograms and converting them to pounds to display (they apparently did something like that for British users measuring themselves in stones), but that is just a guess. If it is NOT a conversion/display issue and the weights are being captured as slightly different, that could be another source of the problem.
Summary of typical fixes I've seen, read about, and heard from tech support:
1. Ensure Aria is on a Smooth Level Surface: Place scale on a smooth and level surface such as bathroom tile, laminate, or hard wood. Tile may be preferred. Consider using a level to ensure chosen surface is level. Avoid carpet.
2. Ensure Body Fat % is Being Captured: According to tech support, BF% must be captured by the scale for the weight to be mapped to a user account. BF% may not be measured if 1) you aren't barefoot, 2) the scale surface is too dirty (wash it with a soft cloth and rubbing alcohol), 3) your feet are too dirty or too callused (consider a good wash or a pedicure), or 4) the BF% sensor is broken (this apparently happens).
3. Ensure Aria is sufficiently close to WiFi Router: Some have reported success after moving their scale closer to the router. This may be a coincidence or more reflective of a difference in the flooring, as it is hard to explain why connectivity issues would manifest in weigh-ins being relayed consistently and correctly but the user not being recognized.
4. Change Aria name to match your user initials: I don't have any idea why this would help, but some feel it has.
5. Update/Verify Fitbit Profile Settings: Make sure your profile settings show a weight that is consistent with what the scale currently reads; make sure the height and gender that is correct (I'd speculate that this affects how BF% is calculated, but that is just a guess).
6. Reassign or Remove all Existing Guest Weights from Log / History: I.e. Go through prior weigh-ins in the app or on the website and either remove or assign to a user all Guest measurements.
7. Alternative to 4 -- Extreme: Delete ALL PRIOR WEIGHT MEASUREMENTS. I believe you'd have to do this via the website because I don't think the app will show you the full record of measurements.
8. Reassign your weight from Guest to your Account Five Consecutive Times: Weigh yourself on the scale, allow it to call you a guest and sync online to your profile, then reassign your weight from Guest to your account. Repeat this process 4 more times (for a total of 5), at which point you should be recognized.
9. Remove Battery and Reassign Weight: Remove a single battery, wait at least fifteen full seconds (maybe go with 30 to be safe), and then repeat option 8.
10. Reset Aria using Pin Hole on Underside: I did this by inserting a paper clip end in the hole while a single battery was removed, reinserting the battery, and then removing the paper clip. I was told simply inserting the pin for 10 seconds while the scale was off (one battery remove) would do it, but that didn't seem to work for me. When I did it this put my scale into "Setup Active" mode, and I had to use the app to try to set it up again (and at the moment I can't get it to see any networks .. so tread carefully here). I was cautioned by tech support that if you insert the pin too long it may erase the actual program on the scale permanently so that the scale no longer does anything.
11. Try Your Luck with a New Device: Life is short. We should probably put a cap on how much time we spend troubleshooting "automatically logs my weight". The Withings Cardio and Yunmai Smart Scale have been mentioned by others as potential alternatives that may be able to link to the Fitbit ecosystem. I'm the solo user of my scale and I've been reassigning my weight from guest for about five years. I wish they had a "default to user X" option instead of default to Guest.
12. Pay Attention to Your Invitations: Some folks said they felt like how the registered for Fitbit affected its ability to recognize them. E.g. who sent the invitations, did the use the website or app, etc. Again -- not sure why this would be a reason, but FYI.
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