I've installed this app on splunk 7 enterprise for windows and I thought it was a bug, so I now downgraded to 6.5.3
I still don't see connection failures. I checked the firewall logs and I see drops, so the port is blocked. However, my search only shows successes.
I took a peak at the py files and I see I am supposed to get a "999" status, but I only see "200"s.
I don't have experience with this TA, but it sounds like you're getting incomplete data. i'd first check the source to confirm those drops are being logged where Splunk can see them, then verify your inputs are set to collect that source properly.
That said, I notice the app is only known to work (according to splunkbase) up to Splunk 6.6, so I'd be concerned about its ability to function on 7+. If this app is something you have a need for, I'd recommend contacting the author to see if they have plans to update it.