One other idea regarding the external drive. It probably won't resolve the issue, but it's not too hard to try and it's simple, so I'd be inclined to give it a stab.
If your external SSD drive has a power connector separate from the data connector, which some do -- that is, it's not relying on USB or similar for all its power -- and it hasn't been powered down since you hit the problem with your Arch installation, I'd try shutting down the computer, then killing the power entirely to the drive. Then power it back up, and start the computer again.
I have, before, seen USB-attached devices that manage to get themselves into some sort of funky state. Normally, rebooting the computer resolves that, but with devices with an external source of power -- which can be the case for external drives -- I have seen devices sometimes not cleanly reset when the computer does and stay in a bonkers state.