We have noticed some reports from players who are seeing an error message when opening chest rewards. And there is also an actual bug that prevents the Open Animation from playing and showing the rewards that sometimes is triggered if there is a network connection issue like packet loss.
The good news is that the reward is paid to your account and that it is a visual issue why it is not shown to you; you absolutely got the contents of the chest added to your account so worry not!
It is unfortunate that you could not enjoy the fun of seeing your rewards, but we advise you to force quit the game on your device and it will show up when you start Vainglory again. Note that the chests will not show-up again, but the rewards will be displayed correctly on your game when you start the game after following the steps below.
Force Quitting on iOS:
Double-click the Home button to see your most recently used apps.
Find the app to close
Swipe right or left to find the app that you want to close.
Swipe up to close
Swipe up on the app's preview to close the app.
Force Quiting Android Apps
1. Open Settings App
2. Scroll down and tap on ‘Application Manager’
3. Scroll down in the ‘Downloaded’ list and tap the name of the app
4. Tap ‘Force Stop’ to fully close the application on your device