I have two connections set up, with ping testing to test the service being online. I disconnect the plug from one line. The connection does not failover to the second line. I go to diagnostics and I am able to select the port that is disconnected and test ping. The ping goes through(!). I then run traceroute- sure enough- the traceroute goes out over the second connection. So the log doesn't show the connection having gone down, but the system is obviously aware that it has and is routing the connection back over the second line.
Further diagnostics would be required to determine what is occurring here.
Best to contact support with a Technical Support Report taken at the time of the issue, and from there the issue can be diagnosed.