I think Inien’s questions are quite important, which spell (or spells) did you have left in your deck? Especially in arena, where typical decks do not have many spells in them, it is possible that there was no spell left in your deck to discover. Also, remember that the Cleric of Scales draws the spell it discovers (it is not a copy), so if you had more than one, the first one might have drawn the only spell you had left, and later when you play the second one it had nothing left to discover.
Please share your screenshots using the instructions in the sticky, but since a key piece of information we might be missing from the screenshots is the content of the rest of you deck, I am not sure there will be much to conclude from them. At least we would know if many people report similar issue with similar hands as yours, that there may be something which requires fixing.