I suspect you’ve renamed the default deck. I recommend you locate the disappearing deck in the browse screen sidebar, rename it to ‘Default’, and then move the cards in it to a newly-created deck with the name you want.
I suspect you’ve renamed the default deck. I recommend you locate the disappearing deck in the browse screen sidebar, rename it to ‘Default’, and then move the cards in it to a newly-created deck with the name you want.