This issue can happen for the following emails:
Contact Customer
Draft order invoice
Customer account invite
Abandoned checkout
Abandoned POS checkout
Payment Reminder
B2B access email
Some of the Shopify notification emails require a special {{ custom_message }} liquid tag to be included so that Shopify can insert any text that you can add just before sending those emails manually from the Shopify admin.
Note: Shopify preview will show a message as a placeholder for the {{ custom_message }}, such as: "Welcome to our shop, hope you enjoyed the experience" but your real emails won't contain that phrase.
Make sure that your email template contains either the Introduction text section or the Custom message section in the editor. Those sections contain the code needed to insert the message. To insert one of these sections in the email, do the following.
In the editor, click the "Add section" button at the bottom of the sections list on the left.
Select either the "Custom message" section or the "Introduction text" message and click "Add".
You can also drag the section in the list of sections to move its position in the email. Keep in mind that the custom message will appear in the email where this section is placed.
Optionally, if you don't want either the Introduction text or the Custom message section in your template because you have a Text section instead, what you may do is simply add the required variable {{ custom_message }} inside the text section:
