So, the last time I tested the changing of an email on an ‘allowed email list’, my experience was that I was immediately signed out, the original email no longer worked, and I had to sign in with the new email. The process seemed to work as expected. I would have to test again to see if any of that has changed.
The fact that you got a blank screen and could still sign in surprises me. Were you still able to sign in after a few minutes after glide re-synced the sheet? Was your test using the script or by directly editing the whitelist email through the app?
In the old post you referenced I mentioned the use of a user id instead of an email to link data and to use for filters. A lot has changed in a year with security, and with the addition of row owners, it now requires the use of an email in each sheet for data that needs to be secure, so there is a need for something, such as a script, to update the email throughout the spreadsheet. On the other hand, if you are not actively using the Roles feature, you could assign the role to the user id column in the user profile, use that ID instead of email in all your sheets, and then assign row owners to that ID column in each sheet. That way you only need to update the email in the user profile sheet, and that can be done without a script by instead allowing the user to edit the email themselves in Edit mode (if it works).
I will have to play around again, but I really think it should have signed you out once the email is changed in the user profile/whitelist sheet. In my tests I was more focused on an admin type user “blacklisting” a whitelisted user. I didn’t test as the user changing the email themselves. I’m guessing it maybe caused an app crash since the email didn’t match on the local device database and couldn’t sync back to the glide server database. That’s why you were able to refresh and sign back in with the same email.