Submitting an upgrade order that switches a subscription to a new service template brings Control Panel down.
Caused by: java.sql.SQLException: ERROR: duplicate key value violates unique constraint "subs_resources_uni" Detail: Key (sub_id, rt_id)=(1292762, 1000532) already exists. Query: UPDATE subs_resources SET rt_id = ? , path = ? , sub_limit = ? WHERE rt_instance_id = ?
The log also shows an outage of chief SC:
ERR [SYSTEM 1:24025:b2fe3b90 pleskd ]: [ SCMonitor::svc] sc_id chief:/usr/local/pem/libexec/chief-lin.so(3)  dead ERR [SYSTEM 1:24025:b2fe3b90 pleskd ]: [ SCMonitor::svc] restart 1 service controllers
The issue is known under internal ID POA-109970 (chief sc core dump when uprgading subscription to incompatible template)
Analyze the set of resources on the source and destination service templates and avoid the situation, when 2 resource types, based on the same resource class, in the source ST are mapped to a single resource type on the same ST in the target ST. Add one or both source resource type to the destination ST as a solution.