TypeError: null is not an object (evaluating '(a?e.shadowRoot:e).appendChild')

My Home Assistant version: 0.113.1

My lovelace configuration method (GUI or yaml):

yaml What I am doing:

not sure, seems to coincide with <strike>pages using markdown. or conditional cards, though I cant state is a 100% match</strike> Entity Cards containing other (custom) cards. Really difficult to pin it down. Has been here for a very long time though. Below is an example that, even without the styling of card-mod, causes the error to appear.

What I expected to happen:

What happened instead:

Minimal steps to reproduce:

# The least ammount of code possible to reproduce my error

type: entities
entities:
  - type: custom:hui-element
    card_type: markdown
    title: |
      Home Assistant --> Google Assistant
      Voice commands
#    style: |
#      ha-card {background: url('/local/various/google_assistant.png');
#               background-size: cover;
#               box-shadow: none;
#               margin: -16px -16px 0px -16px;
#               }
    content: |
      Ok/Hey Google,

# End of code

Error messages from the browser console: in Safari (Mac)

Unhandled Promise Rejection: TypeError: null is not an object (evaluating '(a?e.shadowRoot:e).appendChild')

in Chrome (Mac)

Uncaught (in promise) TypeError: Cannot read property 'appendChild' of null
    at c (card-mod.js?v=2.0:1)

---

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[Mariusthvdb]

thanks!

[zibous]

Same Problem here:

card-mod.js:1 Uncaught (in promise) TypeError: Cannot read property 'appendChild' of null
    at c (card-mod.js:1)