Hi,
Welcome to the Microsoft Q&A forum!
Based on your description, the problem only occurred in Outlook. You can check if there are any Add-ins in your Outlook. Especially some anti-virus Add-ins. Try to disable all add-ins to see if this fixes your problem. You can also run Outlook in Safe Mode instead.
Another possibility is the color of the font, sometimes the font color is the same as the background will look like the text disappeared. You can change the font color to automatic.
About details, please refer to:Outlook Not Showing Email Body/Content? 5 Fixes To Try
Please feel free to contact me for any updates. And if this helps, don't forget to mark it as an answer.