Just upgrade some rb to 7.18.2 (hap ac2, rb951ui, rb951g, omnitik, hap ac lite, hap lite, rb2011uias), all having the same problem:
after rb reboot, sometimes sstp client not auto connect to the server. But after few hours, it will suddenly connected.
No logs about sstp client trying to connect, and no login attempt in server logs. Revert to 7.16.2 fix the problem.