A similar thing is happening to my client's site:
klekfm.org. I've tried that .htaccess snippet as well as increasing the memory. I've even read an article on here about seeing if it was a plugin causing it. I deactivated plugins and tested and still got timeout errors. I've tried every solution I can think of and looked up. I've even tried another plugin that's suppose to "fix" the issue and that didn't work (Divi Tweeker). What do you do if plugins aren't "causing" the issue?
P.S., a unique issue with me is that when the page/post DOES work, I can mess with the modules.