I’ve tried to scour the forums for something similar to this issue but I haven’t found anything that actually applies as of yet. I’ve been forced to change the deck on every new card I’ve created because I didn’t want to cause an issue and now it almost seems like it’s spreading to other decks 
Now certain decks have just stopped displaying new cards in general. I have tried updating. I have tried opening without add-ons. This problem occurs on every platform, AnkiWeb, Anki mobile, and the desktop application. I love the platform but I no longer know how to fix this issue. Thanks.
For your first issue, you likely have ‘deck override’ turned on. Cards are being placed in the "Default" deck - Frequently Asked Questions. For your other issue, if you’re reaching your review limit for that deck, Anki will stop introducing new cards until you manage to clear the backlog.