Time templete errors in logs

Configuration
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These sensors work good but I notice I’m getting this error in the logs.

How to I set a default?

Error while processing template: Template<template=({{ as_timestamp(states('sensor.date_time_iso')) | timestamp_custom('%I:%M%p') }}) renders=114>

homeassistant.exceptions.TemplateError: ValueError: Template error: as_timestamp got invalid input 'unknown' when rendering template '{{ as_timestamp(states('sensor.date_time_iso')) | timestamp_custom('%I:%M%p') }}' but no default was specified


  # Minimal configuration of the standard time and date sensor
  - platform: time_date
    display_options:
      - 'date_time_iso'


  # Build on the standard sensor to produce one that can be customized
  - sensor:
      - name: MyDateTime
        state: "{{ as_timestamp(states('sensor.date_time_iso')) | timestamp_custom('%A %B %-d, %I:%M %p') }}"
        icon: "mdi:calendar-clock"
        
      - name: MyTime
        state: "{{ as_timestamp(states('sensor.date_time_iso')) | timestamp_custom('%I:%M%p') }}"
        icon: "mdi:calendar-clock"

      - name: MyTimeShort
        state: "{{ as_timestamp(states('sensor.date_time_iso')) | timestamp_custom('%I:%M') }}"
        icon: "mdi:calendar-clock"
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