tape adapter is probably fucked. get a new one.

If it was plugged to a mixer who has 2 inputs for stereosound, then you should use a twinheaded cord. Stereo cables - at least in my experience - don't work with mixers if they use only one input. Using mono cords solves my problem but I don't use panning.

Or perhaps the cord/stereo is only using one stereo channel, check to see if the cord you're using is stereo.

weird..
When I said headphones earlier I meant to say my tape adapter for my car, and that was giving me issues.
Couple days earlier I had awful sound issues that were also lead me to believe of panning issues.

Yet, they work with my actual headphones...

I guess that venue's sound system blew/and or the sound guy hated me.
I feel really silly now.

It's possible the one side on your headphones crapped out, actually. test them with something else, like your laptop.

Try different headphones?

I recently panned everything to the left and nothing was coming out, as if I muted the channel.
This was not the case when I unplugged the headphones and the speaker was emitting the sounds like normal.
I tried this on two different gameboys and the same thing happened.
ssSSooo I'm assuming this is a software issue?
I'll re-flash it once I get the chance.
Reasoning why I'm posting this is to see if this has happened to anyone else.