Attempts to edit HTML blocks with several lines of code is nearly impossible without losing patience and giving up. You can not scroll up and down the HTML code viewer with the scrollwheel, scroll bar on the right, or by selecting the code and panning up; see this gif:
The only method I’ve found that allows me to edit HTML code more than 30 lines or so is to click inside, and arrow-key my way back to the top:
I wish there was a proper viewer for large blocks of content, especially HTML with dynamic Bubble content. I imagine clicking a button near the default content viewer that pops open a large/resizable and responsive modal window that is designed to handle large amounts of text. I’ve ran into this issue with normal text content but HTML editing seems very buggy in comparison. I have the same results in Chrome and Firefox.