Most probably the issue is not REBAR.
Does the symptom occur in both modes, UEFI or Legacy (CSM On)?
EDIT: Bad luck… a huge gap in hw generations. Did you reset CMOS and tried another PCIe slot?
There’s a beta bios H.B0 (V17.11 11/23/2016)… but only refers as notes, supporting external TPM2.0 module.