Bad news, the new SSD is detected by BIOS, by BTX loader but not by BSD
Hi raulfg3, sorry to heard that, however you could try and update the HP T510 to latest BIOS and re-try, also you could try another 2.5" SSD/HDD to test, as some chipsets/disk controllers don't play well together causing unexpected behaviors.
For the HP t510 Flexible Thin Client
I found the following info regrading latest BIOS:
"HP Compaq Thin Client Series System BIOS (786R11 BIOS) v1.05 Rev. A 2.3 MB Jul 2, 2013"
Another option was to try UEFI, though is temporary disabled in RootOnZFS due console output issues, but I believe the HP T510 don't feature it at all.