I have the Sky bb SR 102 router and not sure last time it had a frmware update, but for the last 6 nights ( early morning) between 1am and 2 30 am, my BB has gone down then connects again. Not sure whats going on because its solid during the day, ADSL not fibre
It may well be Sky's Dynamic Line Management (DLM) that has triggered this!
I remember when I had Sky ADSL just over a year ago around 1-2 am my internet would disconnect for at least 10 days. Wait another 4 days or so and see if after 10 days this behaviour stops!
I highly suspect it is DLM because at that time it is very suspicious for it to happen. Make sure you leave your router on at all times to allow for the line to be stabilised. After that it may magically stop by itself and it may be that there is nothing wrong with the router.
For example moving to Plusnet ADSL their DLM would trigger 10 days at exactly 5:45 am which is different from the Sky ADSL DLM schedule.