I noticed that my ` and § keys had switched places and wasn't sure when it started. I checked keyboard and language settings, even changing everything to US but to no avail.
I was wracking my brain then remembered about installing Karabiner Elements to adjust keyboard mappings. Even though the only key I had modified was caps lock these other keys were reversed when Karabiner was running.
Fortunately, you can perform simple modifications to remap the "grave accent & tilde" and "non US backslash" keys so keyboard normality has been restored.
This pleases me no end as I like having all my keyboard shortcuts for Magnet running off of caps lock mapped to command+control+option+shift.