You are asking for “get unlock ability” on an unlocked phone. So as I understand it from the links I gave, this points to “device state” more than anti-rollback. That command does not actually query the roll back index.
This has been an issue previously and it crops up online quite often. There are a number of other posts linked to mine and @olli0371’s on this subject maybe one of those would shed a slightly different light.
In what state is your OEM unlock at this time? Here is a different case Revert back to stock OS and relock bootloader - #4 by aibd