Just the other day, I was engaged with an Enterprise customer while he was experiencing an SSL Cert déjà vu, it was disappearing from the IIS binding. It was interesting for sure, and hence the preclude for blogging it!
First thing first, what's the error message here? An event similar to the following is logged in the System event log:
Log Name: System
Date: 3/25/2017 5:33:23 PM
Event ID: 15300
Task Category: None
SSL Certificate Settings deleted for Port : x.x.x.x:443
The error description does match with the symptom, so it's a good start for now. The problem occurs because of a legacy SSL certificate hash property interfering with the current SSL binding, resulting in the correct binding being deleted.
The fix was rather simple, if you know where to look at. We located the following property in the applicationHost.config file and deleted it:
<property id="5506" dataType="Binary" userType="1" attributes="None" value="AJKFOIEURKJEJNOIAUFJDJF=" />
An iisreset is not necessary after the above change, but recommended.