Everytime i use tags on a post, and click save, i get a runtime error, my site goes down for abour two minutes, then comes back, no tags of course added to the post, anybody has that problem or knows what could it be?
This a plugin conflict. Do you run Worldfence? Some accelerator plugin?
Disable the plugins one by one until you find the cause. Could also be a theme issue but rarerly.
Mostly it is a plugin doing that.
The Wordpress included health check shows something?