macbookandrew on "[Plugin: EWWW Image Optimizer] Ewww running when loading frontend pages?"

Yeah, flatfolio is regenerating images like crazy, that's causing your load issues. Report a bug with them, and reference that pastebin you posted, as it will show them where the images are being generated. They should be caching any images they generate to disk, and then checking to see if the image exists before generating a new one.

However, EWWW shouldn't make the page load slower with debug tued off, but here's my suspicion on why it is:
Enabling debug mode tus off background optimization, which uses asynchronous requests. Those background requests can be stalled if a plugin is using sessions improperly (WP core doesn't use them at all), as it will "lock" the session in the background bringing all processing to a crawl until all of those background requests timeout.

So we'll leave the flatfolio issue to their devs to cleanup, but here's what we need to do:
Can you search through your entire WP site codebase for any instances of the session_start() function and let me know if you find any?
If you have command line access, you can use rgrep (or 'grep -r'), otherwise see if you can find a way to recursively search through all the files for that command. Your webhost might be able to run a quick search for you also.