with TCE 15 efibootmgr -v results in "EFI variables are not supported on this system."
It works with TCE 13 (on the same EFI x64 system and same EFI settings)
I found a link about changes in efivar to efivarfs, in recent versions of efibootmgr, could it be that this is related:
The efivars module has been replaced by "efivarfs" now (wiki.debian.org/UEFI#efibootmgr_and_efivar).