I have the same issue. It makes creating email campaigns endlessly frustrating and time-consuming. It scrolls so fast I am never able to place the image or text where I want them to go, they end up at the bottom of the email. I am considering changing to a different service because I have been having these same issues with every email I create for months.
I apologize you too are having this experience! Have you tried working in a different browser as suggested previously in this thread? Are you able to see the pink line when attempting to add a block? We have seen cases where users can control their scrolling by moving the mouse slower to land on the spot to drop the element. You also have the option of double clicking the block so it's added to the bottom of your campaign. You can then use the drag and drop icon to the right of the block to drag where you want it.
I'm ready to switch to a different service too. I have been working for hours today and can't produce a document with pictures due to the uncontrollable scrolling!
Customer service has been very helpful when I can't make it work. They've always stepped in and done what I needed from their end. (they create a copy of your email and edit it)