I think I know why the flaky behavior and disconnects are happening though I don’t know how to fix it. The problem has to do with USB 2 vs USB 3 connections.
When an external drive negotiates a USB 3 connection, it uses more power.
USBDeview reports 896 mA for a USB 3.0 connection vs 300 mA for a USB 2.0 connection with my 2 TB Seagate drive.
When I plug in the drive in halfway, it negotiates a USB 2.0 speed connection which uses less power. This connection is very stable for me.
When I plug the drive in all the way to begin with, there’s not always enough power to get the 3.0 connection to work so the drive doesn’t appear. However sometimes there is enough power so the drive appears, but the 3.0 connection is less stable on my Framework and can disconnect.
This is the same with my 1 TB expansion card drive which disconnects often. I eventually started experimenting by connecting the 1 TB drive via a USB-C male-to-female adapter connected to a USB-C to USB-C cable into a USB-C slot in the Framework. I noticed that using a charging USB-C cable with only USB 2.0 data speeds would stay solidly connected. However, when I used a USB 3.2 speed cable to connect it, I would have disconnect problems. This is, in fact, what led me to figure out this important difference in connection types and stability.
Now if anybody can tell me why this should cause problems and how to fix it, that would be the final piece of the puzzle. Shouldn’t the Framework be able to handle these power requirements. Say 900 mA per USB port?