Please raise a service request at Informatica Global Customer Support (GCS) to have this investigated. Finding the root cause of such special problems can take months (and I'm not kidding).
Unless you have extended support you will not be able to open a case with support.
Informatica 9.6.x was end of life a long time ago.
Oh my, thanks for pointing out this one, Paul. My bad, I should have paid more attention to this one.
Thank you for your answers.
We have opened a case at Informatica Global Customer Support.
If we discover something new, I'll update this thread.
Two things just came to my mind:
First, could it be that any infrastructure component (SQL Server, OS of the PowerCenter machine, DB client version... whatever) has been upgraded to a state which is not supported with 9.6.1 by Informatica?
The PAM (Product Availability Matrix) of your 9.6.1 version clearly indicates which versions of which infrastructure software are supported with your 9.6.1 version, and if anything doesn't fit (e.g. trying to run your 9.6.1 repositories on Oracle 19c), then you're in trouble and have to roll back to the former version. Or roll forward PowerCenter to a supported version.
Second, could it be that the DNS lookup for the PowerCenter server(s) has been changed during the weekend? The DNS lookup miust be set up such that a so-called "Reverse DNS Lookup" works; that means, you can not only look up the IP address based on the IP host name but also the other way round.
That's a security requirement; it has been established by Informatica a while ago in order to prevent IP spoofing.