It’s said there are two main causes and solutions:

1) Server timed out and closed the connection.

2) Server dropped an incorrect or too large packet.

I changed these two places in the file “mysql/bin/my.ini”:

find:
innodb_lock_wait_timeout = 50
max_allowed_packet = 6M

change to:
innodb_lock_wait_timeout = 500
max_allowed_packet = 128M

reboot MySQL and Apache, problem is solved.