Plesk shows 502 Bad Gateway while trying to suspend/activate the subscription.
The following message can be found in
CONFIG_TEXT: (104: Connection reset by peer) while reading response header from upstream
Connect to the server via SSH.
Reinstall sw-engine & sw-cp-server packages from https://autoinstall.plesk.com/version/OS/engine selecting your version. For example for Plesk 12.5 on CentOS 7:
# rpm -ivh http://autoinstall.plesk.com/PSA_12.5.30/dist-rpm-CentOS-7-x86_64/engine/plesk-rdbmspp-2.0.1-centos7.735641.15021818.x86_64.rpm http://autoinstall.plesk.com/PSA_12.5.30/dist-rpm-CentOS-7-x86_64/engine/sw-cp-server-2.2.1-centos7.16072715.x86_64.rpm --force
Repair Plesk database:
# plesk repair db
Run Plesk installer and install all the updates or reinstall micro-updates:
# plesk installer