Well, I'm glad to see that I'm not the only one that finds the editor incredibly frustrating. My computer is basically brand new and even after trying some of the steps mentioned above, I'm editing in 7.1 and it's constantly lagging and I'm finding myself needing to refresh the page soooo many times to make really simple edits. It makes me a little nervous to see so many people having the same issue and as far as I've seen, Squarespace hasn't made any solutions. Starting to think building sites for clients on here isn't such a great idea after all.
I'm also having issues with the typing and words showing up over 30 seconds later thing too, so annoying, I'm shutting it all down and coming back later lol.