@Kulam_69 this does not qualify as a valid discussion.  I have converted it to a product question.

I can see that the support incidents you already logged are open and being investigated.

Your listed  dt1-sftp.pegacloud.net URL is internal URL and it is accessible through VPN (private network only).  You have been asked to share the source server private IP details to check whether IP whitelisted or not 

You also confirmed that you carried out testing and its works fine now. 

 I believe any RCA update will be provided by our Cloud support teams.

Solution from the support ticket:

during the call, cloud team noticed that the source IP addresses were different when client attempted to connect to SFTP and SFTP connection originated from these two IP addresses  which were not whitelisted.   Cloud then now allowed these IP addresses as well, and connectivity working after whitelisting these two IP's..