After upgrading Exchange from 2016 to 2019 and Explore Active Directory endpoint, any attempt to modify an account attribute the Identity Manager displays the error message:
Skype for Business Properties pool must be specified
In the endpoint setting I see the field Front-end Poll empty, I'm not sure if before here was any value
Identity Manager 14.x
Some changes in the Active Directory account.
Check the attribute named: msRTCSIP-UserEnabled in the Active Directory.
If it set to true change it to false or no value