Couldn't play spells on minions

I was playing the arena brawl and on my last turn I couldn’t play spells on any minions. I would drag the spell like normal (Android) but nothing would happen.

Did you get any kind of error response from the game, like when the game tells you “That is not a valid target” or “I can’t do that”?

Or did the spell appear to succeed, but then just silently failed with no error response at all?

What spells did you try to cast, and what minions were they?

No error response. Just acted the same way as if I had dragged the spell to a place with no minion, for example. I tried Mortal Coil and Drain Soul. Opponent had 7 minions and I tried on many of them.

The minions weren’t elusive and it didn’t seem like they had any kind of elusive effect active.