lovelace-card-mod: Not working on iOS and sometimes even on Edge

My Home Assistant version: 2021.3.1

My lovelace configuration method (GUI or yaml): GUI

What I am doing: Modified --icon for 3 button cards inside a horizontal-stack

What I expected to happen: Icon to reflect code changes always and on all devices

What happened instead: sometimes a refresh of the browser ( Edge on Win10 ) shows standard icons, mostly of the time it works. Instead it never worked for mobile app ( iOS device ). I have tried with javascript_version: latest as per troubleshooting steps but I receive:

2021-03-07 19:48:12 ERROR (MainThread) [homeassistant.components.frontend] Please remove javascript_version from your frontend config. It is no longer supported

Minimal steps to reproduce:

    card_mod:
      style: |
        :host {
          --icon:
            {% if states('binary_sensor.custom_alexa_speaks') == 'on' %}
              mdi:volume-high;
            {% else %}
              mdi:volume-off;
            {% endif %}
          }

Error messages from the browser console:

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