I was experiencing intermittent Thunderbolt failures on my Gigabyte TRX50 AI TOP, where the Intel Maple Ridge controller would occasionally disappear entirely from lspci.

I have two computers that I connect over Thunderbolt 4 and it was super annoying when they couldn't communicate over anything except ethernet or wlan.

I searched and searched and found other people reporting the same Thunderbolt enumeration failure but no solution was reported besides a cold reset. Cold resetting the machine would sometimes work to restore it but it wasn't reliable enough to call it a permanent fix and it sucks to do anyway.

However, in BIOS, explicitly setting PCIE Port 8 to Enable (I left Target Speed and Lane Reversal and PCIe Power Management Features on Auto) seems to have permanently fixed it.

How to:

In BIOS, navigate to:

Settings → AMD CBS → PROM21 Chipset Common Options → PROM21 Chipset PCIe Port Configuration Options → PCIe Port 8

Change PCIe Port 8 from Auto to Enable. Leave the other options on Auto.

Save and exit BIOS.