Hi there @CamillaAndersen ,
Thanks for posting and welcome to the Community!
There could be a possible issue within the template itself. Thankfully, this article is a good solution for if your email client is pulling in other text for preview text, if you're using the drag and drop editor.
If you're using HTML custom coded templates, please see here for solutions that your developer can try.
As an alternative fix, if you do not want to use the Preview Text field that is located next to the Subject line, you can always add in content within a Text block in your email. It needs to be the first block of the email. If you do not want the text to "show" in your email, then the recommendation is to change the text color to white.
Lastly, did you by chance keyword search your inbox? If you're searching for the email, it's expected behavior that the preview text for the email you're searching for may not always come up. The reason for that is the keyword you search for will also search the body of your email, and that can pull into the "preview" field.
Hope this helped!
Alex
@alex.hong Thanks for some great tips! The HTML preview text hack fixed the problem.
No problem @CamillaAndersen! Glad you were able to find a solution to your problem!