accessing internal application server over slow link

Can you map a network chart for me visibility? Seems like a network issue. 

Yesterday I had to re-install our pfSense router so people could access the application server. I was tired of trying to fine tune our fancy new XG box on a Saturday. The pfSense router is identical hardware, Supermicro intel 2758 quad core. We have a 2 core 4GB RAM XG SW/Virtual appliance license. As soon as the pfSense box was active, the problem was solved. The only thing I can think of is that pfSense utilizes all CPU cores and RAM which are double of what XG utilizes due to the SW license we have.

I'm at a loss. Why would pfSense allow slow connections to access the application server w/out timing out while the XG box would not?

All IPS, application and web filtering on the DNAT rule is disabled.

Actually we are doing the same as pfSense. Simple DNAT with Conntrack. So this should not be a hardware issue or something like that. 

Is this connection UDP or TCP? 

TCP.

The application server also access other external servers that the sw vendor hosts. So, a remote client connects to our application server and portions of the download they are attempting originate from our LAN and portions also originate from externally hosted servers.

So, the application server is a proxy for a portion of the data that's downloaded by the client.

Regardless, pfSense has no issues,

XG terminates downloads when accessed over high latency connections but does fine with other low latency connections.

TCP.

The application server also access other external servers that the sw vendor hosts. So, a remote client connects to our application server and portions of the download they are attempting originate from our LAN and portions also originate from externally hosted servers.

So, the application server is a proxy for a portion of the data that's downloaded by the client.

Regardless, pfSense has no issues,

XG terminates downloads when accessed over high latency connections but does fine with other low latency connections.

This is impossible to troubleshoot. You should perform a tcpdump and look at the packet level to find the root cause of this behavior. 

when we purchased the Sophos system, we also included "Professional Services (Central) - 5
hour Remote Assistance" but I cannot figure out how to use this support option. Can you kindly explain how i can get a Support Technician to connect to a screen sharing session to help me troubleshoot?

Hello Dan,

Thank you for contacting the Sophos Community!

Could you please provide me with any Case Id you have with us or your Account Name, so I can look for you and direct to your Account Manager, so he can arrange your Professional Services hours! 

Regards,