Level One FBR-1412TX freaking out after speed upgrade

I've changed my VDSL connection from 8/1 Mbit to 10/2 Mbit a few days
ago. Coincidentally, a few hours later, my Level One router started
behaving strangely. Namely, after a few hours of normal performance,
its log starts filling up with entries like these:

2007/04/04 11:43:35.51 M r={+++++++++++++++++++++.+++v+++v+.++++++++.
+}3
2007/04/04 11:43:44.51 M r={v++++++++++++++++++++.+++++.+v++v+++++++.
+}3
2007/04/04 11:43:46.51 M r={+++++++++.+v++++.+++v+++++++++++++++.+++.
+}4
2007/04/04 11:44:14.51 M r={++++v++++++++.+++++++++.++.+++++++++.++++
+}4
2007/04/04 11:44:17.51 M r={+++++++v+++++.+++++++++++..v++++++++++.++
+}4
2007/04/04 11:44:29.49 M r={++++++++++++++++++++.++v++.+++++++++.+++.
+}4
2007/04/04 11:44:31.49 M r={.++++++++v+++v+++++++++++++v+++.++++++.++
+}3
2007/04/04 11:44:49.49 M r={.++++++.+++v++++++++.++++++++.+v+++++++++
+}4
2007/04/04 11:45:09.49 M r={++++.+++++++++++++++++++++..+++.+++++++++
+}4
2007/04/04 11:45:49.49 M r={++++.+++++++++++++++..+++++++++.+++++++++
+}4
2007/04/04 11:45:52.49 M r={+++.+++++++++++++++++++.+v+.+++v.++++++++
+}4
2007/04/04 11:45:59.49 M r={+++v+++.+++v+++++++++++++++.+++.++++++++v
+}3
2007/04/04 11:46:35.48 M r={.+++++++++++++++++++.++++++++++.++.++++++
+}4
2007/04/04 11:46:40.48 M r={+++++++++++++.++++++.++++v+++++.+++++++++
+}3
2007/04/04 11:46:43.48 M r={+++++++.+++v+.++++++.++++v++++++.++++++++
+}4
2007/04/04 11:46:55.48 M r={++++++++++++++++.+++.++++.+++++.+++++++++
+}4
2007/04/04 11:46:59.48 M r={+++++++v++++++++v+++.++++++.++++++++.++++
+}4
2007/04/04 11:47:18.48 M r={+++++++++.+++v+++++++.+++++++.++++++++++.
+}4
2007/04/04 11:47:20.48 M r={+++v++++++++++++v++++.+.++++++++++++++++.
+}3
2007/04/04 11:47:40.48 M r={++++.++++++++v++++++.++++.++++++++++++++.
+}4
2007/04/04 11:47:41.48 M r={v+++.+++++++++++++++.++++++++.++++++++++.
+}4
2007/04/04 11:47:50.48 M r={v+++.++++++++++++++++++++++++.++++++++++.
+}3
2007/04/04 11:47:58.48 M r={.v+.+++++.++++++.++++++++++++++++++++++++
+}4
2007/04/04 11:48:14.48 M r={+.++v++v+++++.+++++++++v++++++++++++++++.
+}3
2007/04/04 11:48:23.48 M r={.+++.++++++++.+++++++++++v+v++++++++++++.
+}4
2007/04/04 11:48:25.48 M r={+++++++++.++++++.++++++++.++++++++.++++++
+}4
2007/04/04 11:48:31.46 M r={+++v++++++++++++.++++.+.+++v+.+++++++++++
+}4
2007/04/04 11:48:47.46 M r={++++.++++.+.+++++++++++++.++++++v+++++++v
+}4
2007/04/04 11:48:53.46 M r={+v+.v+++++++++++++++v+++++v+++++.++++++++
+}2

The connection works fine for a few more hours (log being filled with
such entries, and also a few regular ones), but later on the router
freezes completely.

After restarting it, the story repeats itself. Even resting offline
and off-power for 2 hours didn't change a thing. I'll try a complete
reset today, as well as a firmware re-upgrade if needed.

Any ideas as per what may be the reason? Could it be the higher speed,
or is this just a coincidence?
(The number of concurrent TCP+UDP connections is not an issue, I've
sorted this out a few years ago. )