Logitech K750 keyboard: § and < have switched places
It sounds like a keyboard type glitch, the machine thinks it is ANSI instead of ISO or vice versa.  See if this helps:

Sometimes a machine will forget which type keyboard is attached, with the result that certain keys get transposed from what the user expects. The fix for this is run the Keyboard Setup Assistant again. Sometimes there is a button for "Change Keyboard Type" visible in System Preferences/Keyboard. If not, you can try trashing the file

sudo mv /Library/Preferences/com.apple.keyboardtype.plist /Library/Preferences/com.apple.keyboardtype.plist.orig


Another possibility may be to open Terminal and type:

sudo open /System/Library/CoreServices/KeyboardSetupAssistant.app/Contents/MacOS/KeyboardSetupAssistant