My RUT240 did not connect to the internet via the WAN. Ping 188.8.131.52 worked, Update worked, so it was connected, i supposed some trouble with DNS. Half year ago i found the solution to that problem in this forum: I had to uncheck "Disable NAT". But after months, whenever the router was switched on, the connection startet fairly good, got slower and slower, until finally after one or two hours, there was no more internet connection at all again. After a lot of experimenting and investigation, i found the solution: I have unchecked the "connection health monitor" (which seems to check the connection by pinging a given IP-Adress, i had entered the 184.108.40.206, i a certain rythm). After unchecking, my connection ist far better then ever before und fully reliable.
A known bug in the routers firmware? Is the health monitor useful for anything?