Hi Patrick,
some additional reproductions showed two cases of failure to find the MSIX capability:
Case1: HW reports PCI_CAP_ID_SLOTID (0x04) and PCI_CAP_ID_EXP (0x10), but not PCI_CAP_ID_MSIX (0x11).
Case2: HW reports no capabilities at all
A retry (after a short delay) in both cases reports the MSIX capability alright.
Thanks,
Alex.