Shun
状元
On an iPhone 13 Pro running Pleco with the large flashcard database, I now managed to catch an empty flashcard listing screen. It only happened once, and seemingly randomly. Exiting the category and re-entering it brought the flashcards listing back. This must be another tricky to reproduce bug. At least you'll know it exists. 
What it looked like after switching back in:
What it looked like after switching back in: