Thanks for clarifying. It looks like your theme is set to dark, and you use Menu / View / Enable white background, correct?
Message loading / processing for display has recently changed somewhat, so yes, things could break a little...
However, I'm unable to reproduce the issue here with my sent messages.
Is there any way you could send me the exact source of this sent message (or any other which exhibits the issue), as an attachment?
Here is how to do this in GMail web mail:
https://support.google.com/mail/answer/22454?hl=en