Ever since downloading the Anki app, my decks and subdecks have been deleting themselves every time Anki syncs. Cards have also been removed from the decks that have not been deleted. Even after I deleted the app this problem has still been persisting and is very frustrating.
It can only happen if you deleted something on one device and downloaded that change to another one.
Anki tries to match your cloud collection with the local collection you’re syncing to. If you look at your decks in ankiweb.net and every device you use, do they match after a sync or do they show different things?
The thing is that I never made the changes that are occuring on any device. I deleted the mobile app and I am still encountering this issue. The decks also delete themselves randomly, where it is different each time. I’d like my anki to go back to the way it was before I ever bothered with the mobile app. When I had the mobile app, I would only ever do reviews- never make deck changes and I was having these problems.
Maybe backups will help you. Backups - Anki Manual
It’s hard to tell you exactly what your issue was, but the neither of the apps goes around randomly deleting your decks, notes/cards, or review history.
Let’s get your desktop collection stable and then you can think about whether you want to use AnkiMobile again. First, run Tools > Check Database. Then, if there are still things you can’t find, say more about where you’re looking for them, and what you’re not finding or what you’re finding instead.