They failed once the PC was placed in the case.
They failed once the PC was placed in the case.
Consider using a different SATA cable to verify the LAN port, just in case any pins were accidentally bent inside it.
Looking at this broadly, the key differences lie in how components are put together and housed. One issue could be misalignment during assembly, like a bent pin as noted by TofuHaroto. Another possibility is that metal cases might cause shorts if connections aren't properly secured. If mounting without standoffs is attempted, unintended short circuits could form across the board's back.
I've already tested another SATA cable and everything looks okay. The stands were put in place, except for one that was missing since I couldn't locate a 9. One was installed properly based on what I could see. When I removed it from the case again, I had to burn the LAN and SATA connections because they weren't working at all, even though the rest functioned normally.