Nexus Siege Bug

Just played a Nexus Siege game and found that there is a bug when I'm on the defending team after the enemy team defends first. When the timer starts going backwards and there is less than 3 minutes remaining on the timer, I cannot use any of the elixirs. The game lasted for 18 minutes when I was on the attacking team, which means the game lasted at least 15 minutes when I was on the defending team and I still could not use any of the elixirs. Please check if it is a bug. Thank you.