The left half of my ergodox doesn't work :(

[PhyterJet]

I've lurked around here for a while, but never really felt the need to register, 'till now.

This was my first proper hardware project, first major soldering project. And everything went well, it worked and it kept working for about 8 weeks, and now the left half wont respond
I ran xev (Xwindows event viewer), and sure enough no scan codes were received at all by my computer. 

I do carry it with me, to university and back home, so maybe a weak solder joint got bumped while I carried it??.
I don't have a soldering iron with me, this Saturday I'll go down to makerspace (hackspace) and try and fix it, even if I have to re-solder every single joint.

I did buy a multimeter though, so I checked that the TRRS cable works, the board connections between the TRRS cable works, and that 5v is getting to the left hand side.

so it's probably the IO expander, or the teensy??, i dunno have like zero experience, and i don't want to start randomly probing stuff, in case I short something and break it more.

Does anyone have any advice?

[BlueBär]

Due to the transport a weak solder joint might have broken. Check all solder joints (focus on the ones that are not for the individual switches first, because if one of them would be broken just that single switch wouldn't work) and redo the ones that look like they could use some love. If you aren't sure you should post pics of the PCB and your solder joints.
My guess is that something's going wrong at the I/O expander or the TRRS connector since the entire left hand is failing. Be aware that if it is the TRRS connector the 5V might arrive on the other half while the data doesn't if the other pins of it aren't working correctly, so don't skip checking the connector.