HTTP requests to internet web server through Link Controller fail with packet resets

I've come across the solution and it's not on the Link Controller. The web admin of the remote site moved the web server to a new co-lo facility and reconfigured the site but forgot to "white list" our public IP blocks that the clients were connecting from. I'm not exactly sure what security software/hardware is in place at the remote site but it was blocking inbound requests from our public IP blocks after a specific threshold was reached from each source IP. The threshold was not triggered by individual hosts, but when multiple clients initiated requests (behind a PAT), the "security software/hardware" would block the requests.

 

Thanks, everyone, for your input and assistance with this! After this issue though, I wonder what could've been tested to determine that the issue was on the remote end without input from the remote admin? NMAP? HPING?