I also noticed the same issue that the automation was not triggered on a very short press when the trigger in the automation is set on the entity for the shelly switch. This is solved by using MQTT, I use the automation below.
It will only trigger if the previous trigger was more than 5 seconds ago.
alias: Doorbell push notifcation
description: ''
trigger:
- platform: mqtt
topic: shellies/doorbell/input/0
payload: '1'
condition:
- condition: template
value_template: >-
{{ (as_timestamp(now()) -
as_timestamp(states.automation.doorbell_notification.attributes.last_triggered
| default(0)) | int > 5)}}
action:
- choose:
- conditions:
- condition: state
entity_id: switch.doorbell_chime
state: 'off'
sequence:
- service: notify.notify
data:
message: Someone at the door (chime off)
title: Doorbell
data:
ttl: 0
priority: high
color: red
default:
- service: notify.notify
data:
message: Someone at the door (chime on)
title: Doorbell
data:
ttl: 0
priority: high
color: green