Zhonya and fiendish codex

Just played a ranked game as Morgana support. Literally could not complete items containing fiendish codex. I bought all components for zhonya, but would not let me finish it despite having more than enough gold. Tried using stopwatch to see if that made a difference; did not. I purchased stopwatch from store - in case that matters. I sold components, tried buying again; could not purchase. Used one component to buy a different item; it worked. Tried buying twin shadows using my codex instead; could not purchase completed item despite having the gold for it.

Zhonya is kinda a core item for morg, so I'd say this is a pretty serious bug if she can't purchase it in ranked games. The fact I also couldn't buy twin shadows suggests it might be something to do with fiendish codex since that component overlaps for both items. I could buy shurelya's though, so it wasn't just a completed items bug.