The most likely issue based on everything you just said is the app’s timeout. I have heard multiple complaints like the one you described and that is the most likely issue. My current app (1.4.4) is far too aggressive with the timeout (3 seconds on testing if the IP is valid). I am resolving these issues in the upcoming app update by increasing the timeout.
For the record, when using the direct IP method in a browser, there is no timeout at all.