Still getting problems …. as I configured watchdog (mode: restart interface, Period 1m, hostotocheck: 8.8.8.8, addrefamily: ipv4, checkinterval: 5m), last night I disabled it to make a try, even it was working since when I configured it (see MF286D - regular disconnects)
At boot this morning, no valid connection (even if some staistics were present on the interface), then I manually restarted it and it worked.
Not very clear to me where to look to (isp problems, some broken configuration).
I saved dmesg&logread outputs just after I got connection.