Is there a glitch on this card? all it requires is 2 zombie cards on ur field / and or graveyard. so many times where I do have 2 zombies on the graveyard after activating grass is greener or just 2 zombies in general and it doesnt work but it does the next turn. Also it doesnt work sometimes when you synchro summon and ur monsters get sent to the graveyard. The card doesnt have any limitations other than having 2 zombies in the graveyard or field so why it doesnt work sometimes?
also regular Spectralsword i think also doesn't allow dragon specialsummon after its graveyard banish effect too...
Maybe one of the monsters you played before has a restriction like: "You can't Special Summon other monsters for the remainder of the turn".
Eg: Shiranui Spectralsword Shade has an effect that can summon 2 banished Zombie monsters if you sacrifice that card, but you can't Special Summon for the remainder of the turn, except other Zombie-type monsters. Therefore, you can't use in that turn Dragon Mirror to summon Dragonecro.
Read your cards ffs... see what the person said below me. (See guys? I don't repeat what was already said. This regards the big nerds who like to repeat answers just to show off.)
The restriction is on other cards you played.
Example : If you summon Shiranui Squire & used her effect to SS a spectral Sword, you cant SS other monster except Zombie type.