I use Outlook on my S9+ and have an odd problem. HTML emails do not display fully. I could get 1/5 to 3/5 of it but rarely the full email. My other mobile devices do not have this problem. I have compared settings between them and everything is set the same.
I was originally going to try that but was worried it would mess up my Secure folder work account. Happy to report it didn't! Now I wait for an email...
Do you have the Developer Option turned on? I found this solution on another forum. When I turned off the Developer Option, the emails that would not display fully did. Even when I turned the Developer Option back on, it still worked.