I have a different issue - my Samsung SSD was detected via external SATA/USB plus. It allowed me to format it, even install fresh OS, but as soon as I swapped it with my old HDD on my early 2011 Mac, the only drive recognizable by system was a Recovery drive. Mac does not detect my SSD via internatl SATA connection. My HDD works ok, so I assume it’s not a case of SATA cable. I reformatted it again, without installing anything via exteral plug, then tried again, and this time my mac did not detect any drives at all, not even Recovery.
Any hint on why it’s not detectable?