Slow download to company's website, except on VPN

I recently signed up for Internet service with Magenta (formerly T-Mobile) in Vienna, Austria. It's a basic 40 down / 10 up home service, and generally works well and as-advertised.

EXCEPT!

I am also starting a new job at a company that serves a web app hosted in AWS (us-east-1). After cutting over to Magenta, my web calls to static files and API calls to this web app are taking a very long time. For example, it takes between 2-5 minutes to download a 6 MB file. I am the only one at my company who is experiencing this, and no customers are reporting any issues!

This evening, I tried downloading the same 6 MB file while connected to an Austrian VPN offered by NordVPN, and the download took 2 seconds!

Any thoughts about what might be happening to me, or suggestions on what to try to debug/isolate the issue? Thanks!