I recently got the parts for building my Umbrel node and have had the same issue with the SSD disconnecting. I shutdown the system when this happens, and it happens A LOT (see it happening with the % sync’d going down to zero and no more blocks being processed). I am using a Sandisk Extreme Pro 2 TB external drive. Since most of the reported problems with SSD disconnect seems to point to a power issue for the drive (and I am using an official Raspberry Pi power adapter), I have ordered a powered drive enclosure and a 2 TB Samsung SSD drive and will try using that (and use the Sandisk 2TB drive for something other than Umbrel), and hopefully that will fix the problem (have tried to use different Sandisk cables, different Raspberry Pi (4 Model B 8 GB) USB ports. It is hard for me to believe that powering an external SSD drive makes the Raspberry Pi/Umbrel software barf like it is doing. Hope that the new hardware (powered SSD drive enclosure) that should arrive shortly overcomes the problem. Only good thing about the problem was that it helped me learn more about the system, SSHing into the Umbrel server, running command line commands to see the system status, etc. But then again, would have liked to just get the node up and running, although not sure whatALL I will do with it once I get it up and running. Guess learn more about Lightning, and if I find that my Umbrel server is stable enough, guess I will connect a wallet to it and try to route transactions through it… I know - Umbrel is beta, not completely developed - so give it a break. But still…
Did some additional google internet research and found that the problem with Raspberry Pi’s loosing connectivity to external hard drives is a known problem (not just in the Umbrel world) and it is power related. So, what I think should happen is that Umbrel should let people who are in the process of purchasing hardware for an Umbrel node, know that power issues could come up with external drives connected to the USB ports, and that it is recommended to have a powered drive enclosure to overcome the problem (or use a powered hub - apparently some Raspberry Pi users have found this to work to overcome the problem with loosing external drive connectivity).