I'm working on getting sticky bucketing to work with fallback attributes. I have an experiment that is setup to use the anonymized id (that all users have) as the fallback attribute and the email (which only registered users have). When the user starts as anonymized and then logs in with an email account, sticky bucketing works as expected. They continue to see the first variation they had with their anonymous id. The opposite does not work, however. If a user is already logged in and accesses an experiment for the first time, and then logs out, and accesses the experiment again, they will see a different variation. This seems to be because, on the first experiment access, Growthbook only saves the variation from the email address to the sticky bucket server. It seems that it should also have the anonymous id together with that first variation. Does this make sense or am I missing something? Thanks

Your understanding is correct. Sticky bucketing "upgrades" from fallback to primary, but not the other way around.

Thanks, Ryan. Is there a reason for it not working "the other way around"?

Hi there. We don't support this natively due to ambiguity about who the user actually is post-logout. Granted if the device is not shared among multiple users then it's probably safe to say it is the same user; however in this case, its probably better to experiment on a deviceId attribute rather than userId or anonymousId. If desired, you can also rig up your own persistent uuid that survives logging out and use that as the hash attribute.