Unlike some others, my upgrade went well. However, I still see this message, presumably carried over from the previous version:
WARNING: /var/www/html/plugins/API/API.php(401): Notice - compact(): Undefined variable: idGoal - Matomo 3.6.0 - Please report this message in the Matomo forums: https://forum.matomo.org (please do a search first as it might have been reported already)
I have disabled the Goals module just in case our lack of goals (heh) was causing it. (Narrator: “It wasn’t.”)