So this post was originally going to be a call for help, but the solution was so easy and obvious, I figured I'd repurpose it to share my little nugget of wisdom with anyone who needs it.
If the "My Feed" web part looks wrong (i.e.: missing usernames, document names, etc.) in Teams. all I did to resolve the issue was: remove the web part > publish the change > re-add the re part > publish the change.
THE SHAREPOINT HOME SITE WITH WEB PART:
VC BEFORE FIX:
VC AFTER FIX:
Like I said, probably obvious for many of you. Either way, I hope this saves someone a few minutes of troubleshooting.