Apache2 500 Error

I’m using hestia with apache2 and nginx.
when sending a request without full headers (like a web browser), the server returns a 500 error.
In logs:

[error] 3594488#3594488: *863613 upstream prematurely closed connection while reading response header from upstream, client:…, server:…com, request: “GET / HTTP/1.1”, upstream: “https://…:8443/”, host: “…”

how to change the hestia web templates, so that it allows requests without full http headers?
or is the problem something else?