You are using Safari, right?
The technical story:
Safari doesn't support StereoPanner so everything will be in mono.
It does support a normal Panner, but you can't set their position "over time" so they are somewhat useless.
Yes, I know there's a nice shim. This works but it is too slow.
The solution:
Use another browser like Chrome or Firefox. There you'll have full stereo.

You are using an iPhone, right?
   -> Your 'silent-mode' switch at the top right side is on.
The technical story:
For some weird reason Apple has decided to play 'normal' media on websites with the 'media' audio setting, but webAudio with the 'ringer' audio settings. This is why when you have your silent-mode switch active, you still hear e.g. video on websites, but you won't hear anything in BassoonTracker.
The solution:
Switch the silent-mode switch to inactive.

Midi is only fully supported in Chrome.
Is it enabled in the options?
Is your midi device working in other midi-enabled software?
Also make sure you play some audio first using the regular keyboard, the audio needs user-interaction to be allowed to start.