SSO has been failing for multiple users.
There is a work around which is to reset the SAP password but this is only temporary.
The Server they were using was SSO SNC but the SAPUILandscape file located at \AppData\Roaming\SAP\Common was missing the tag sncname="" and sncop="9" was set to sncop="-1",
Adding the tag sncname with the SAP Service name and changing sncop to 9 make it work for that particular server with which they were facing the issue.
In addition, a port needed to be open with SNC secured CPIC and RFC Communication within the firewall.