Help needed - TCP packets to my own router's previous IP

Hi all,

I should start by saying that I am no network expert. I’m a programmer by trade, and a bit of a jack-of-all-trades when it comes to IT.
I’m investigating an issue where, on our simple network - not even using a domain - some computers take between 20 and 60 seconds to respond to the first call to wininet.dll InternetOpenW function.

I checked all the settings I could think of. Someone suggested I use Wireshark to see which servers were “hanging” on the machines that exhibit the problem.

I didn’t notice any server hanging per se. However, there are some TCP packets to our network’s external IP address. It’s as if those calls, are delaying/blocking the application’s traffic.

The strange thing is, the destination IP address is not in use at the moment - I use a Cisco rv320 router which allows for double WAN connections. The IP address is the backup internet service, but it’s not connected to the router at the moment, and as a matter of fact, that connection is not setup at the moment, so the router doesn’t (or at least shouldn’t) know about it. That address has been used 3 weeks ago when our primary internet connection failed however (but the router was reconfigured after that).
Also, if the problem came from the router, I would expect all machines on the server to have the same issue, but it’s not the case - wireshark captures from “unaffected” machines don’t show these packets (at least in the few seconds that I capture.

I’d upload a capture but I can’t as a new user. any idea what could be causing this, and more importantly, how I can fix it?

Thank you!