How do you know you've been without connection all night? Did someone send you an emal at 3am that you received only at 7am? Maybe it woke up every 30 minutes, connected, checked emails etc, then disconnected again and went into a deep sleep. When you woke up and checked it in the middle of that period, it had to go and connect.

Please note that I am merely speculating, I do not pretend to have an answer. I do not need to wait for the night, my Jolla loses the connection several times during the day. And I have to restart network connections at least 3 times a week.