WebServer doesn't work until I switch the php version from 7.1 to 7.2 or 7.2 to 7.1

i'm a newbie here, I have an issue with a server that I couldn't find an explanation. the webserver stops working untill I switch the php version i'm using ISPCONFIG webpanel and I should conenct go to sites and switch the php version and than the web server starts working again.

let me know if u need more informations.

thanks in advance