This is probably the weirdest macOS issue I have ever had. At some point on my personal MacBook Escape. Yup, still rocking one of those terrible bad boys from 2016.
That Apple have had to replace all the internals of twice. I guess they’ve lost money on me on that one.
Here is the issue: in some apps lines the current like got duplicated when I git the up arrow. After a lot of head scratching, cussing and frustration I discovered the problem by looking over everything in the keyboard settings. Turns out I had mapped the “Convert to traditional Chinese” service to up arrow.