Funny enough, I just upgraded my router a couple weeks ago, and the Hubitat hubs hated Auto with the new router. They were sluggish, and would disconnect occasionally. When I set the Hubitat to Fixed 100, they were lightning fast again,
So my advice would be to try both, and see what works better in your situation with your equipment.
Thank you all!
It seems that I had set the Network speed to "Fixed 100mbps" at some point.
I have changed back to "Auto negotiated" and it is now working fine