VnC server shows connection via Cloud, but iPad Viewer frequently cycles through login attempts unsuccessfully

Internal (same) network/direct IP connections from iPad VnC Viewer to Windows PC running VnC Server works just fine 99.9% of the time.   

However on roughly 1/3rd of the connection attempts to use iPad Viewer from remote locations when connecting via Cloud to access the same PC result in it showing a successful login, whilst the iPad VnC client messages show the following;  Connecting RealVnC services > Searching Network for VnC server > Preparing Desktop....  Then repeating the same messages multiple times until the iPad app crashes and closes.  Meanwhile VnC Server shows multiple successful logins by the same user.

I've had limited success deleting the app and reinstalling it on the iPad, but that doesn't work but about half the time.  Seeing this issue on the iPad whether I'm connecting it via another network or via cellular network/Wifi connection.

Any ideas?

Thanks in advance,

-Tim