I seems that nobody except for Linux (for some not yet determined reason) is having issues with retrieving EFI variables on this hardware, and one could potentially classify this as a bug in `efibootmgr` as well (due to how it handles creating the new entry in unknown conditions).
In either case, Linux is the only thing affected by this, so in real-world setups Linux is going to be the only boot option that is available while the boot menu is in a broken state.