Review cards not showing up (despite being displayed?)

Hello everyone! Thanks for taking your time to help me out here.
The problem I am facing, is that the cards I reviewed are not showing up properly (although they are shown until you want to review them).
It’s a bit tricky to explain and please bear with me, I have never experienced something similar in all my anki life. That’s the deck in question.

And here are the screenshots

(it shows the correct amount of reviews here)

As soon as I want to review them though

it only shows 1 review card for each topic only! :frowning: )

It’s a shame, since the deck is really well made!
I’ve created many decks myself and have studied from various other decks as well, and did not encounter said problem so far.

What can I do about that? Is the deck bugged or am I missing something?

Thank you very much for your help guys!

Please see Studying - Anki Manual

Thank you so much dae! Made my day c: