I must have had a glitch in refreshing my pages when I tested both Katex and Mathjax. I tried again with Mathjax and the equation label/number is not showing anymore with that same code, just like you. The scrollbar only shows when the label shows up, and so it looks like it is Katex related. Can you reproduce the issue with Katex set in the settings?
I was not talking about the zoom feature. Which I believe does not work with Katex anyway?