Server blocking cloudflare data centers

I was working on a website earlier it was working fine. But now it is show a 404 error and my ssl encryption mode is flexible, when i chance it to full or full (strict) it shows [525] error one day next day it works fine then next day again it shows [525] error.
Means when encryption mode is flexible it shows 404 error and when full or full (strict) then website works on alternate days.
I don’t why is this happening i so i asked for help in cloudflare community they give me an answer which i didn’t understand.
I am attaching a screenshot of that

2 posts were merged into an existing topic: 404 error