Spells sometimes deal more damage sometimes less damage than they should

I recently played a game and I had double rabadon's T2 Syndra. Her spell was, according to the tooltip, was supposed to deal 1050 damage to any unit hit. I kept playing and noticed that several units in the 600 hp range would be hit by her spell and it would only deal like 50% of their hp as damage when it should. There are other times I notice that certain aspects of the game don't deal damage correctly, either dishing out too much damage or not enough. I would send a video of the bug I just experienced but you can't, as far as I know, download replays of TFT games so I don't have it.