Gmail will cut off and display [Message clipped] View entire message at the bottom of your email if the email is larger than 102kb.
This limit can be reached if there is a large amount of content (this includes formatting code and images) in your email. You may also see this happen after sending yourself multiple test emails with the same subject line because they will appear as part of a conversation thread in your inbox and later messages will be clipped.
To avoid this, it may be best to revise and reduce the amount of content in your email. Review our article on HubSpot Email Tool Best Practices for some guidance.