The mt91-fsx motherboard is common for the R181 and R281 ThunderX2 servers. Gigabyte has provided a release of the BIOS which included better support for nVidia GPUs and PCIe Gen4. This is version F28. Below is a link to this BIOS file available via your web browser. Please use this version in future builds of R182/R281 ThunderX2 system builds.
F28 is the firmware version that include the PCIe Gen4 issue fix. Below is the link to download image. For your information.