500 error after upgrade from 6.5.3.4 to 6.4

hey everyone,

so I installed an update couple of days ago, after it was done the website didn’t work so I entered dev mode and saw that I should change the premissions of private.pem and public.pem from 644 to 660 or 600, after that the website was working but couple of hours later I started getting emails saying the website was down, so what’s happening is that the store appears online for some people and others get the 500 error, the 500 error disappears if the store is in debug mode but i can’t keep it like that for everyone

anyone has an idea?