Microsoftjdbst56 Thank you for the feedback! I've located your specific report and routed it to the Identity Team. We will follow up if there is any additional information needed or updates/insights to share.
-Kelly
Microsoftjdbst56 The team has investigated and can see from the feedback report submitted, on MS Edge launch, the user got signed in with the secondary AAD account on the machine.
ConfigureOnPremisesAccountAutoSignIn policy mentions that MS Edge will give preference to AAD accounts over on-premises account.
Enable the use of Active Directory accounts for automatic sign in if your users' machines are Domain Joined and your environment is not hybrid joined.
The behavior currently being experienced is to be expected and the change to use secondary account was made in MS Edge V86.
The current suggestion from the team is to consider removing the secondary AAD account from machine.
To provide a little more information, we are evaluating/investigating creating a new policy so users will not get implicit sign-in with secondary AAD account if ConfigureOnPremisesAccountAutoSignIn is configured.
bin_da - Please take a look at this post and see if it helps your situation as well.
Thanks!
-Kelly
Kelly_Y Thanks for your response.
So in our testing we saw that both AAD accounts and personal accounts are taking precedence over the on-premise AD account. We had to remove all traces of both accounts in order for the AD sync to work.
In our testing scenario, we removed the AAD account from Access work or school in Windows 10. After doing so and closing Edge, deleting the the User Data folder from AppData\Local\Microsoft\Edge and relaunching Edge, we found that the browser was then trying to sign in using personal gmail/hotmail accounts. We're not certain where these logins were coming from possibly the Microsoft Store or other Microsoft resources. On one system, signing out of all Microsoft resources and clearing the Edge User Data folder allowed the sign-in/sync using the AD account to work successfully. On another system, signing out of all resources and clearing Edge User Data folder did not resolve the signing with personal account. On this system we had to completely delete the Windows user profile to enable sign-in/sync with the on-premise AD account.
So in order to make this functionality viable for our enterprise, there needs to be the ability to force the sync to use on-premise AD account without the need of deleting the Edge User Data folder and/or Windows user profile.
Microsoftjdbst56 Thanks for following up with your testing results! The Identity Team has confirmed what you've seen is to be expected.
The auto sign-in policy works in this way:
In this case, once the AAD account was removed, step “3” took place. So like you noticed it is necessary to remove all of the MSA and AAD accounts from settings.
We appreciate your feedback! It is helpful to hear directly from users as they are investigating the new policy.
-Kelly
Kelly_Y Do you have any timeframe for this:
"To provide a little more information, we are evaluating/investigating creating a new policy so users will not get implicit sign-in with secondary AAD account if ConfigureOnPremisesAccountAutoSignIn is configured."
Microsoftbenhealy Hello! Sorry, no ETA yet. I can follow up here once we have updates to share. 
Is this blocking the adoption or deployment of MS Edge in your organization?
-Kelly
Kelly_Y Yes it is stopping us deploying currently.
Our Windows 10 devices are hybrid joined and our Security/Architecture team are not endorsing cloud sync. As On-Premises sync doesn't work with this setup, if we roll out our users will be forced to export and import their bookmarks whenever they log into a new computer or get re-imaged. Not as user friendly as they are used to with Favourites and folder redirection.
