I'm having similar problems trying to access a remote MySQL database.
Everything works fine from my home network here in the UK and from a friend's network in the US, but not via the school's network.
The school's IT people and myself have run all sorts of tests to try to pin-point the problem, all to no avail.
I've even taken the school's router and Raspberry Pi home and connected it to my network - where it works fine. So that sort of eliminates some of the key pieces of hardware and the NR flow.
At the moment I've given up on this issue as I used up so much time trying to sort out the problem.
