Alert rules not executed after upgrading PMM Server running as Docker container

User impact:
The user has an empty Alerts list and existing Alert rules are not evaluated

Preconditions:

• Start PMM Server 2.17 by executing commands:

docker pull percona/pmm-server:2.17
docker create --volume /srv --name pmm-data percona/pmm-server:2.17 /bin/true
docker run --detach --restart always --publish 443:443 --publish 80:80 --volumes-from pmm-data --name pmm-server percona/pmm-server:2.17

• open PMM, enable Integrated Alerting and create an alert rule

template: 'PostgreSQL connections in use'
threshold: '1'
duration: '1'
filters: 'service_name=pmm-server-postgresql'

• Wait for alert to appear in Alerts tab

Steps to reproduce:

Execute next commands:

docker stop pmm-server
docker rename pmm-server pmm-server-backup
docker pull percona/pmm-server:2.19
docker run -d \
   -p 80:80 \
   --volumes-from pmm-data \
   --name pmm-server \
   --restart always \
   percona/pmm-server:2.19

open PMM and go to Integrated Alerting -> Alerts

Actual result:
There are no Alerts from IA

Expected result:

Alerts should appear as they existed before

Note:

• Alert Rule is present
• /etc/ia/rules folder is empty

Workarounds:

• Create another Alert rule (or maybe some update an existing one) - after this action rule will appear in /etc/ia/rules and in 3 mins Alert should appear