Try to disable "expire" plugin in dovecot.conf to reduce Dovecot dict server workload with below steps:
*) Comment out "expire =" like below:
dict {
#expire = db:...
}*) Comment out "expire" plugin related settings in dovecot.conf like below:
plugin {
...
#expire = Trash 7 Trash/* 7 Junk 30
#expire_dict = proxy::expire
...
}*) Restart Dovecot service, and see whether it happens again.
WARNING: Please do replace sensitive info before pasting config files. e.g. password.