Keyboard commands work during boot, but stops working after booting?

I've got an interesting quirk of a problem here that I cant quite figure out.

The keyboard for my 15" mid 2015 Pro Retina works during the boot sequence, or at least all of the keyboard commands/shortcuts do. I can boot into safe mode, I can boot into recovery, I can boot into external, I can reset the PRAM, I can reset the SMC with all of the various key combinations. So the keyboard clearly works and is communicating on some level.

However, as soon as one of the boot options has loaded the keyboard wont take regular input anymore (like entering a password), except it still is able to SMC reset (instant shutdown on key activation).

I've tried inserting other keyboard data cables and those keyboards are running into the same issue, so it's not a bad keyboard data cable. External keyboards work fine when plugged in, but that's an annoying solution having to carry around an external keyboard.

Any ideas on how to fix this besides replacing the logic board? It's just so strange that it clearly can work but refuses to actually work after booting. Any help is appreciated, thanks!