Microsoft is continuously improving Office 365 SharePoint Online. Most of the changes are somewhat announced and documented somewhere.
For example, this SharePoint Blog post mentions a few improvements recently made and rolled out (or at least are in progress to roll out):
Obviously, the issue you are facing appears to be a new feature which is according to Microsoft under development but not yet rolled out.
For an official list of Office 365 features, you might want to check the Office 365 Roadmap page:
It looks like the change you are seeing is listed under "IN DEVELOPMENT" as "Custom Themes", which shows a screen capture with the profile picture instead of the user display name on the top right of the suite bar.