I’m sorry to hear you’re going through that with your website.
When I was going through it, I felt like I was going crazy! When I’d contact my host service they would just offer tips for optimization (which was not the issue. I mean, it’s all great info! But not pertinent to that experience at the time). Adding to the mystery even more was (1) pingdom and other speed tests did not indicate the slowdown (what the heck?!) and (2) it did not happen to 100% of visitors (especially those with Mac/Safari). However MOST people who visited/tested my website – in different geographical locations, different internet providers, Mac & PC users, mobile and desktop, different browser types – experienced the horrific loading times. To make matters even more confusing, there was one stretch of time (a few hours) where the problem seemed to resolve itself. But then the slowdown returned, with a vengeance.
I deactivated every plugin, followed all the optimization advice, checked query monitor… all to no avail. On top of everything, only one of my websites was experiencing this dreadfully slow (20 – 30 seconds on a good day) loading time. I could not find one single consistent variable.
I contacted my host (several times), my internet provider, my theme developer (Tom is always there for me!), and the developer of the one plugin I used that had not noted that it was compatible with the most recent WP update.. still no improvement.
Trust me when I say I can feel your pain!
The good news is that it’s not happening anymore, yay!!
The less-good news is that I *still* do not understand what the problem was. However, I can tell you that the resolution happened in two stages:
1) I contacted my host (Site Ground) again, and this time the customer service rep “added some rules to htaccess” (per the chat transcript), and instantly the backend (/wp-admin) of my site was fast again. 🙂 I didn’t see any improvement in the front-end, but I was so happy to be able to at least access my site without it timing out.
He insisted that both front end and back end should’ve been fixed, and of course (as was the case before), the speed test indicated the lightning-speed loading time I usually enjoy. So I ended that chat hoping the rest of the problem would resolve itself in time.
It didn’t, lol.
2) I contacted Site Ground yet again late the next night, pretty much in tears, pleading desperately for a solution that did not involve “optimization,” haha! I chatted with a customer service rep, and FINALLY my problem had been solved, once and for all, woohoo! I believe there was one small thingy (not the technical term, lol) in my php configuration that he was able to change… but for the life of me, I cannot find my copy of the transcript to be able to refer back to and let you know exactly what it was. I was probably so thrilled that it was fixed that I forgot to select the option to send myself a copy. :/
I know this doesn’t help you diagnose (much less fix) the problem. But hopefully it points you in the same direction that lead me to the answer.
Hopefully this doesn’t come across as knocking Site Ground. I have had a very positive experience with them and highly recommend them to anybody who asks. Their customer service is awesome, and their uptime is unparalleled! I don’t blame them for the length of time it took to get to the bottom of the problem because – as you well know – it was so tremendously mysterious and unusual.
You *may* find some temporary relief if you restore your site from before the problem began (if you or your host have a backup).
Good luck with everything!!
And THANK YOU, TOM, for allowing us to continue this thread here even though this is NOT A GP ISSUE!! 🙂