I just registered with the forum to thank you from the bottom of my heart for sharing this. I was having the exact same error issue on my parity drive and was using SATA splitters in exactly the same way, and of course it turned out that was the issue. I was tearing my hair out trying to figure out why a perfectly good brand-new drive started suddenly giving me read errors yet passed all SMART tests and worked just fine in another system. Put it back in, secured the SATA splitter, and now it looks like it's working normally again. What a wonderful, supportive community this is!