From my reading of the UEFI spec, much of the language assumes one EFI system partition per device, for example see the capsule updating language on page 262 of

From my reading of the UEFI spec, much of the language assumes one EFI system partition per device, for example see the capsule updating language on page 262 of the version 2.4 spec. The directory \EFI\UpdateCapsule is checked for capsules only withing the EFI system partition on the device specified in the active boot option determine by reference to BootNext variable or BootOrder variable processing. and later The system firmware is not required to check mass storage devices that do not contain boot target that is highest priority for boot nor to check a second EFI system partition not the target of the active boot variable. There's no accounting for two ESP's for one device, and how to resolve the ensuing ambiguity, which one is the primary one? Are you certain Windows updates distinguish between two EFI system partitions, should an update need to update the Windows bootloader or its config?