Not Able To Collect Gold Rewards For Achievements

I was in one of my rounds today when I won the achievement for defeating 5 Railroad Guns. The popup on the screen told me of the achievement, with a button that said "Collect Your Reward". I clicked it and it took me to my Achievements screen. However, where I normally click the button below finished achievements to claim my Gold reward, neither the achievement icon or the Gold button were there. The Gold was not automatically added to my account either, as my Gold balance did not change. I scrolled down on the Achievements screen to where the achievement was listed, and there was no button to claim the Gold, it just showed the amount of gold I would receive by earning the next level of the achievement.

What do I do? I want to earn the Gold I deserve.