I hade a Rite of Belzenlok 0/6 defender (+prevent damage) token out. The opponent was using “God Pharaoh” and his first ability which multiplied it. The cards the opponent was playing were not flying or unblockable. My defender did not and could not block them.
You might want to take a closer look on the number of black gems on the board; The clerics instantly lose their Defender the moment there are not enough black gems on the board.
But if this problem is consistent, yeah, check with support.
The Khenra doesn’t add unlockable to Greg’s creature, rather it adds “cannot block” to your defender but there is no symbol for it. Also it’s a permanent effect…