Literally just
<input type="number" value="0" step="1" />
and it jumps by two for me on clicking both up and down (fine for arrow keys).
https://codepen.io/chandlervdw/pen/qBBdgZp?&editable=true
My coworkers are running the same version of Chrome as me (77.0.3865.90) and it jumps by one for them. The only difference is that I'm running Mac Catalina. Safari and Firefox are fine. How is this possible?