Hello,
This should just be a temporary error and is probably not related to your cards not showing up.
Regarding your missing cards, please follow these steps:
- Reset local changes: How to Reset Local Changes
- See this tutorial to correctly configure your deck and unsuspend cards. You may just have a limit on new cards, or your cards might be suspended: How to Get Started Studying
If this does not resolve the issue, please give me more information about the problem you are facing. Which deck is it? Did you just download the deck? Please send screenshots of what you see.