I had this issue for 2 full days...
I have cleared all the caches, site/browser
I have disabled the manager compress_js/css
I have disabled staticache
I have disabled some plugins
I have reinstall the same version like an upgrade,
I have tried to upgrade to latest one,
I have install a fresh one with same version, and tried to combine my site like an upgrade (didn't work)
Like I was about the tier myself...
I remember my domain was using cloudflare !
I ve login cloudflare, pause the service and BAM!!!
Suddenly it all came back...
For those who had the same error like this
"get rid of the cloudflare!"
Now I have paused all the cloudflare services in it,
because if It happens again some time later,
I would forget the reason and will try to solve it all from beginning
I hope it saves you as well...