I’ve got the DisplayPort expansion card in the right rear bay, DIY edition, Batch 1. It worked fine for the first couple of weeks. Then one day after leaving the computer off for a few days, I turned it on and the card wasn’t being recognized (normally it shows up in the “Safely Remove Hardware” menu in the external device taskbar item). I tried rebooting and moving the card to a different bay, and nothing really helped, but then eventually the card just started working again in the original bay. Since then it’s happened a few more times on its own, sporadically. I also seem to be able to cause it fairly consistently by unplugging a DP cable from the port while the laptop is running.
I’ve tried rejiggering the EMI stickers on all four bays, but it has happened again since then.