Not able to buy items

My last game I played kayn top expecting to be able to go full lethailty for some sick one shots, but sadly that wasn't able to be done. It was due to some random bug that really lost us the game. I do not know why, but the game would not let me buy any AD items what so ever. I could buy health, armor, mr, ect, but just not any ad. However i did manage to fix it around 15-20 minutes in where i pretty much sold my dagger wondering if i had 1100 gold if i could buy it. Then magically everything was unlocked. Did i not read something in fine text or is this a new bug where you cannot buy any AD until you begin to sell your stuff?