I am new at this, so this is my case.
I am getting this error on my Wordpress site and I need someone to point me out where to search the problem. I know that is written in a log file and here it is, but I need just a recommendation where to search next.
tail -f /var/log/apache2/error.log
[Wed Nov 06 17:37:34.338255 2019] [:error] [pid 7783] [client 192.168.0.167:55833] PHP Warning: mysqli_query(): Couldn't fetch mysqli in /home/example/public_html/wp-includes/wp-db.php on line 2007, referer: .php?post_status=publish&post_type=post&lang=sq
[Wed Nov 06 17:37:34.338540 2019] [:error] [pid 7783] [client 192.168.0.167:55833] PHP Warning: mysqli_errno(): Couldn't fetch mysqli in /home/examle/public_html/wp-includes/wp-db.php on line 1902, referer: .php?post_status=publish&post_type=post&lang=sq
[Wed Nov 06 17:37:34.338756 2019] [:error] [pid 7783] [client 192.168.0.167:55833] PHP Warning: mysqli_error(): Couldn't fetch mysqli in /home/example/public_html/wp-includes/wp-db.php on line 1929, referer: .php?post_status=publish&post_type=post&lang=sq
[Wed Nov 06 17:37:34.339084 2019] [:error] [pid 7783] [client 192.168.0.167:55833] PHP Warning: mysqli_real_escape_string(): Couldn't fetch mysqli in /home/example/public_html/wp-includes/wp-db.php on line 1172, referer: .php?post_status=publish&post_type=post&lang=sq
[Wed Nov 06 17:37:34.339421 2019] [:error] [pid 7783] [client 192.168.0.167:55833] PHP Warning: mysqli_query(): Couldn't fetch mysqli in /home/example/public_html/wp-includes/wp-db.php on line 2007, referer: .php?post_status=publish&post_type=post&lang=sq
[Wed Nov 06 17:37:34.339751 2019] [:error] [pid 7783] [client 192.168.0.167:55833] PHP Warning: mysqli_errno(): Couldn't fetch mysqli in /home/example/public_html/wp-includes/wp-db.php on line 1902, referer: .php?post_status=publish&post_type=post&lang=sq
[Wed Nov 06 17:37:34.340001 2019] [:error] [pid 7783] [client 192.168.0.167:55833] PHP Warning: mysqli_error(): Couldn't fetch mysqli in /home/example/public_html/wp-includes/wp-db.php on line 1929, referer: .php?post_status=publish&post_type=post&lang=sq