When Azure ADB2C (AADB2C) is used for authentication on the Dyanmics/PowerApps portal the logout does not redirect the user back to their current location if the Azure AD B2C logout is enabled using the setting Authentication/OpenIdConnect/[Federation-Name]/ExternalLogoutEnabled set to true.

I believe this can work if the portal properly sets the "post_logout_redirect_uri" query string parameter when it calls the AADB2C logout URL. This property is always set to the root of the portal.

I documented this issue in the community post below.

https://powerusers.microsoft.com/t5/Power-Apps-Portals/Dynamics-365-PowerApps-Portal-Azure-AD-B2C-logout-issue/td-p/547256