Error in Query Explain Plugin: Connection error: Lost connection to MySQL server at 'reading initial communication packet', system error: 111(2013)

[joekoforever]

Query Explain, why error?
Error in Query Explain Plugin: Connection error: Lost connection to MySQL server at 'reading initial communication packet', system error: 111(2013)
apache log:
[Mon May 14 16:01:16 2018] [error] [client xx.xx.xx.xx] PHP Warning: mysqli::real_connect(): (HY000/2013): Lost connection to MySQ
L server at 'reading initial communication packet', system error: 111 in /var/www/html/anemometer/lib/QueryExplain.php on line 194, r
eferer: