Optimize-FFU is broken due to the Recovery partition not having a name. dism checks for the presence of a name for each partition and if it doesn't have one, optimize-FFU breaks. The fix is in the ffuprovider.dll in the 25255 branch, which is in the Insider ADK. The public release for that isn't coming soon, and using the Insider ADK requires test signing/test mode to be turned on and secureboot disabled. This causes issues with systems that have virtualization-based security. Due to this, changing the code back to not creating a recovery partition while building the FFU, and creating the recovery partition during deployment and then letting Windows copy in and configure WinRE after. Later this year, whenever the ADK gets released, I'll update the script to revert this behavior.
rbalsleyMSFT