Primary to CAS Database replication is not happening

Question

I am working on building SCCM infrastructure, customer already had Primary site on Domain B and they wanted expand primary site with CAS. As per the design CAS will be built on different domain A, After expanding primary with CAS server noticed Primary to CAS replication (Site data)is not working but CAS to primary (global data) is showing as successful. Replication manager shows Global data initialization percentage shows 96% for almost last 4 days.
Domain A & B has two way trust and all required firewall ports have been already opened.
CAS site installation account and computer object has administrative rights on child primary server and primary DB with sysadmin rights.
Noticed following error rcmctrl.error on CAS server and please suggest
Have case opened with Microsoft and suggested to register SPN for the SQL service but that did not resolve the issue.

Error Message.
Error: Exception message: [Login failed. The login is from an untrusted domain and cannot be used with Windows authentication.~~ OLE DB provider "SQLNCLI11" for linked server "XXXX" returned message "Invalid connection string attribute".

Answer 1

Troubleshooting replication issues is best left to the experts; and since you have already opened a case with Microsoft; that is who you should stick with for replication issues. Provide any logs they require; and continue to work with them to address the replication issue.

That said, you indicated "the customer wanted" to expand the primary with a CAS. What were the technical reasons for doing so? There are very few technical reasons for having a CAS. The only technical reason I'm aware of is total client count. Are they nearing or past 150,000 clients?

If not; perhaps the design may need to be re-evaluated. You don't need another primary + a CAS just because you have multiple domains.