wordpress 500 internal server error

I know 500 internal server error is common error but I tired every thing possible but not sure what is going on
all I know is that I restored my openvz vm and this happened

Howdy,

Anytime there’s a 500 error, that indicates that in $HOME/logs/error_log, there would be an error message. What error message do you see in that log file?

-Eric

Thanks I see errors like this

[Mon Jul 01 14:56:38.142848 2019] [core:error] [pid 637] [client 211.205.129.27:14797] End of script output before headers: index.php, referer:
[Mon Jul 01 14:56:39.070362 2019] [fcgid:warn] [pid 12483] (104)Connection reset by peer: [client 211.205.129.27:14801] mod_fcgid: error reading data from FastCGI server, referer: https://211.206.136.20:2087/
[Mon Jul 01 14:56:39.070501 2019] [core:error] [pid 12483] [client 211.205.129.27:14801] End of script output before headers: index.php, referer: https://211.206.136.20:2087/