@mlauber71 that could be, but it would be very unfortunate 
I’m afraid that this could be something where libmamba doesn’t behave exactly like conda.
For reference, here are some related discussions
- Mamba doesn't work behind a corporate proxy (conda does): download error (56) - failure when receiving data from the peer · Issue #2438 · mamba-org/mamba · GitHub
- Mamba fails to resolve hostname · Issue #17 · opengeos/geospatial · GitHub
- Using Anaconda behind a company proxy — Anaconda documentation
Do you have a proxy configured in your .condarc @mlauber71?