Hi, FireIT. How are you?
When you installed the second vCenter, did you select the "Join existing PSC domain"? or did you create a new domain? Since vsphere.local is a local domain, you can have both domains without any linked mode whatsoever, and then you would need to converge the PSC domains with CMSSO-util. VMware Knowledge Base
If both PSC have the same domain, you may want to check the replication state between them. VMware has a great KB explaining how to do this in Windows or VCSA deployments: VMware Knowledge Base
If all of this is still correct, I would suggest powering off both vCenters, then power off PSCs appliances (If external). Then power on the PSCs. Wait a 5 / 10 minutes for services to start and then start both vCenter servers.
Hope this will solve it
Please keep me updated!
If you are using AD accounts you need to have both sites joined to the domain, to be able to jump, see and manage the resources from both vcenters.
This is the procedure: Join the vCenter Server Appliance to an Active Directory Domain
If thats OK, as Lucas said you can check the status of the replication on a PSC level (a quick test is log in into vCenter A, create an user, go to vcenter B and after a brief time user should be there)
Or the best way to do it is:
Log in into the PSC (or vcenter if it is embedded) and run this comands to verify the psc's partnerts
./vdcrepadmin -f showpartners -h localhost -u administrator
and this one to check the replication status
./vdcrepadmin -f showpartnerstatus -h localhost -u administrator