When typing, after hitting spacebar, I often get an additional space inserted. I haven't seen it happen when using the built-in keyboard, but it happens with two separate external keyboards. As far as suspect software goes, I do have Karabiner installed, though I see the issue even when it isn't running and if it were the issue, I would expect to see it happen when using the built-in keyboard as well.
I've tried two separate brands of USB-A to USB-C dongles for connecting the keyboards, but the issue still happens with both.
I also haven't seen the issue with any other key, only the spacebar. I'm not sure how to go about tracking down a root cause here.
Best Answer
Just found out that this was due to a bad switch, at least on the second keyboard. Both keyboards I was having issues with are mechanical, but it seemed pretty unlikely that they'd both have an issue for the exact same key. I swapped the switch used for the spacebar with another and it's working much better now :)