Gmail clips emails that have a message size larger than 102kb and hides the full content behind a View entire message link.
On clicking on view entire message link your users shall be able to see the entire message. Note that you should ensure that your messages are never greater than 102 kb.
Some of the reasons for message clipping are:
Grammarly extension Grammarly extension doesn't play nicely with SendX text editor and ends up adding its own CSS and HTML which makes email content greater than 102 kb. As a result message shall appear as clipped. To disable it kindly check this article
Multiple text emails Gmail often combines, or “threads,” emails with the same subject line into a single email in your inbox. If you send several test emails for the same campaign then this will lead to the message becoming larger than 102kb leading GMail to eventually clip the message.