only one node works - 107.170.49.232
That's odd. 107.170.49.232 is one of the nodes hardcoded into the client, but so is 37.187.96.15, and as far as I can see, that one is working just fine.
One of the nodes has successfully initiated connections to 5.9.12.149, 203.20.114.252 and 91.121.79.208... so overall there should be at least 5 nodes on the network that allow inbound connects.
Can't see any obvious signs of the three nodes I control banning any peers.
What happens if you change addnode= to connect= in your config,then restart? What does debug.log say about the connections to those 5 open peers?