With X99A-XPOWER-AC and Broadwell-E 6800K, even with latest MSI BIOS to specifically address 1809 issues, I've still not been able to update to 1809.
At least with new BIOS, booting from 1809 media creation tool USB stick will at least make it into windows setup (unlike previous BIOS), but if you boot directly from the media then you can't "in-place update" your installation, only re-install windows losing all apps/settings, which I'm not interested in doing.
If you run "setup.exe" from the 1809 media to update your current installation of windows, it still fails during first phase of boot for me (long hang during first boot, then reboot into rollback).
I've tried replacing all the intel chipset drivers with the originals from MSI for my motherboard as others have suggested, but still same problem.
I've essentially given up on 1809 and now waiting for next major windows version to try update again.
Since I don't buy a fresh motherboard every generation, and I expect a flagship mobo to last at least 5 years with BIOS/driver updates to keep up with Windows and microcode security fixes, I won't be returning to MSI based on my experience with this X99 board.
See this thread for more info about 1809 issues on MSI boards... https://forum-en.msi.com/index.php?topic=309933.0
Maybe some of the suggestions presented there will work for you. Unfortunately they did not for me.