I haven't done any rewiring modifications myself but my best guess is that you used too much solder on one of the pins and when you move the pcb it just barely starts touching another pin causing a bridge. Looking at the
controller pinout diagram by kadano, I don't see how you could have touched the c-stick pinout when rewiring buttons. My best guess it that you somehow touched the symmetrical data line for the c-stick, because I think the -0.7/-0.7 is the value you get when no data is received but don't quote me on this.
Maybe try desoldering your work and see if the problem persists.
If it doesn't, I'd just redo the soldering job more carefully.
If it does persist, try removing all solder that you added on the board in hopes that fixes the issue.