Perhaps the emails have both html and plain text representations, and you've configured your client to only show the plain text version?
This was likely winmail.dat/TNEF[0], Microsoft's proprietary replacement of HTML.
[0] https://en.wikipedia.org/wiki/Transport_Neutral_Encapsulatio...
Granted HTML rendering of email is full of quirks in Outlook
We already have the 365 Web version for that.
Yet another example of Microsoft's failure to hire employees with native Windows development skills, now with the old guard that grew up with Win32 are reaching retirement age.