Many servers exists with many different configurations, so such issues may happen.
1. try disable mod security in cpanel or ask hosting provider to disable
2. change PHP to 7.2 or 7.3, try this php config: http://iwinter.com.hr/support/?p=17307
3. nginx issues guides: http://iwinter.com.hr/support/?p=6975
4. If issue persists also provide cpanel login and admin login via support ticket: https://geniuscript.com/support/
Regarding hosting providers, we using in our demos cpanel version from: