My server is Dell R7525, installed with Ubuntu, rasier2 slot6 pcie4 X16 slot is split into 4 X4, this pcie interface is connected to a 4-slot nvme adapter card, and the 3rd and 4th slots are plugged with 2 nvme solid state drives (Samsung 990pro (gen4) and Western Digital SN750 (gen3)), both of which can be recognized;
However, if the 1st slot is plugged with 990PRO and the 2nd slot is plugged with SN750, SN750 can be recognized, but 990PRO cannot be recognized;
If the 1st slot is plugged with SN750 and the 2nd slot is plugged with 990PRO, 990PRO can be recognized, but SN750 cannot be recognized

slot6 X16 is definitely split into 4 X4, not the split settings
The SSDs are all good
Restarting does not solve the problem
The adapter card is also fine, the problem still exists after changing the adapter card
Reinstalled Ubuntu system, the problem still exists
Replaced rasier2, the problem still exists
The idrac does not have any fault alarm
What could be wrong? It looks like there are 4 split X4s, one is broken?