TypeError: Cannot read properties of undefined (reading 'toLowerCase')

**Describe the bug**
Preview pane doesn't work when creating a new practice.
It does work when opening an existing open practice.
Creating a new practice, filling in the mandatory fields and saving does result in the preview showing up/working.

**To Reproduce**
Start contributing to Open Practice Library and click "New Practice"

**Expected behavior**
Preview of Open Practice submission should be loaded on the right.

**Screenshots**

**Applicable Versions:**
- Netlify CMS version: `netlify-cms-app@2.15.72`
- Git provider: `git-gateway`
- Browser version: `Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/131.0.0.0 Safari/537.36`

**CMS configuration**
```
backend:
name: git-gateway
repo: openpracticelibrary/openpracticelibrary
branch: main
publish_mode: editorial_workflow
media_folder: static/images
public_folder: /images
slug:
encoding: ascii
clean_accents: true
sanitize_replacements: "-"
sanitize_replacement: "-"
collections:
- name: practice
label: Practice
publish: false
delete: false
folder: src/pages/practice
create: true
slug: "{{slug}}"
fields:
- label: Template Key
name: templateKey
widget: hidden
default: practice-page
required: true
- label: Title of practice
hint: The name of the practice
name: title
widget: string
- label: Objective
hint: One liner main objective for the practice
name: subtitle
widget: string
- label: Publish Date
name: date
widget: datetime
- label: Authors
hint: Comma-separated list of case-sensitive github usernames eg., Springdo,
rdebeasi, TdBeattie
name: authors
widget: list
default: []
- label: Tags
hint: Where does this practice live on the Library Loop?
name: tags
widget: select
multiple: true
required: false
max: 3
options:
- label: Validate (Discovery Loop)
value: validate
- label: Value (Discovery Loop)
value: value
- label: Culture (Foundation)
value: culture
- label: Methods (Foundation)
value: methods
- label: Ideate (Options Pivot)
value: ideate
- label: Insight (Options Pivot)
value: insight
- label: Measure (Delivery Loop)
value: measure
- label: Learn (Delivery Loop)
value: learn
- label: Mobius Loop Tag
hint: Where does this practice live on the Mobius Loop?
name: mobiusTag
widget: select
multiple: false
required: true
options:
- label: Discovery
value: discovery
- label: Delivery
value: delivery
- label: Foundation
value: foundation
- label: Options
value: options
- label: Cover Image
name: icon
hint: Image to be used on the home screen and cards for the practice
widget: image
required: true
default: https://github.com/openpracticelibrary/opl-media/blob/master/images/Needs%20an%20Image.png?raw=true
- label: What is this practice?
name: whatIs
widget: markdown
- label: Why do this practice?
name: whyDo
widget: markdown
- label: How do I execute this practice?
name: howTo
widget: markdown
- label: Media Gallery
name: mediaGallery
widget: list
fields:
- label: Media Link
name: link
widget: string
- label: Links we love
name: resources
widget: list
fields:
- label: Link
name: link
widget: string
- label: Link Type
name: linkType
widget: select
options:
- label: web
value: web
- label: purchase
value: purchase
- label: podcast
value: podcast
- label: video
value: video
- label: Description
name: description
widget: string
- label: No. of people required
hin
...