Connection with static IP does not autoconnect Lubuntu 16.04
Solution 1:
Your interfaces file suggests that you want that file to manage your connection. However, in Network Manager, the managed=true declaration suggests that you want NM to manage your connection. You have a conflict. There are too many hands on the steering wheel!
I recommend that you remove the enp3s0 settings from /etc/network/interfaces and set your static IP in Network Manager:
