Hi Marc Rodieck ,
my apologize for the delay, here you can find the answer to your question ;):
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Question: Is it okay to deploy the Azure AD Password Protection Proxy service side by side with other services such as Azure AD Connect?
Answer: Yes. The Azure AD Password Protection Proxy service and Azure AD Connect should never conflict directly with each other.
Unfortunately, an incompatibility has been found between the version of the Microsoft Azure AD Connect Agent Updater service that is installed by the Azure AD Password Protection Proxy software and the version of the service that is installed by the Azure Active Directory Application Proxy software. This incompatibility may result in the Agent Updater service being unable to contact Azure for software updates. It is not recommended to install Azure AD Password Protection Proxy and Azure Active Directory Application Proxy on the same machine.
Reference: https://docs.microsoft.com/en-us/azure/active-directory/authentication/howto-password-ban-bad-on-premises-faq
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Be aware of the incompatibility between "Azure AD Password Protection Proxy" and "Azure Active Directory Application Proxy", in this case is better to have different servers.
Many thanks for your question.
Daniele De Angelis