Missing PCIe Reference clock (Optiplex 7020 Tower)

Our company develops PCIe boards. Only customers with DELL pc's report card detection problems. I have investigated the issue with a DELL Optiplex Tower 7020. The issue occurs in both x1 slots, not in the x16 slot.

The root cause of the problem is that during boot the PCIe Reference Clock is suddenly missing for the x1 slots.

It was observed with BIOS version 1.15.0, as well as with the most recent 1.19.1.

I hope this information could be forwarded to the relevant engineers at DELL so the issue could be fixed.

Below some oscilloscope plot of the reset and reference clock signals of the x1 and x16 slots at powerup.