Corrupted deck? Cards went back to "New" with a longer ID

I have a deck with 3452 cards. I use both AnkiDroid and Anki Desktop to review cards (usually AnkiDroid). Sync’ing works in both directions without problems.

I noticed that for a while I haven’t seen many (dozens) cards I wasn’t doing well on. I investigated, and found that they are no longer in review; nor are they buried or suspended. Since I cannot investigate on AnkiDroid, I looked at the cards in Anki Desktop browsing mode. I found that all those dozens of cards are showing as New, except their number has an extra prefix added. So for example, most actually unseen cards in my deck have numbers like “New #298” etc in the “due” column; but these “broken” cards have numbers “New #7904298” (the 7904 prefix is the same for all of them) in the “due” column. I’ve seen all these cards (many times), and none of them should have graduated yet.

I fear this is still continuing, since some cards I saw recently, are now in this weird state.

The Created date is still the same for all the cards (2020-04-06).

What can I do to get them back to normal, and more importantly how can I prevent this from happening again (I think it might be still going on, since some cards I saw recently are in this state)?

Thanks!

For some reason I cannot upload images, so here’s the text from a card info:

Added 49153-11-03
First Review 2021-06-27
Latest Review 2021-11-20
Position 7904156
Card Type Card 1
Note Type subs2srs-japanese
Deck BOFURI (ep 1-12 w/en)
Note ID 1586200976673
Card ID 1488978224956186
Date Type Rating Interval Ease Time
2021-11-20 @ 17:54 Learn 1 ⁨1⁩ hour 250% ⁨1⁩ minute
2021-10-16 @ 01:18 Learn 3 ⁨1⁩ day 250% ⁨1⁩ minute
2021-10-11 @ 00:37 Learn 1 ⁨1⁩ hour 250% ⁨52⁩ seconds
2021-07-11 @ 17:03 Learn 1 ⁨30⁩ minutes 250% ⁨46⁩ seconds
2021-07-06 @ 21:08 Learn 1 ⁨30⁩ minutes 250% ⁨41⁩ seconds
2021-07-03 @ 22:03 Learn 1 ⁨30⁩ minutes 250% ⁨41⁩ seconds
2021-07-03 @ 04:52 Learn 1 ⁨30⁩ minutes 250% ⁨7⁩ seconds
2021-07-03 @ 04:49 Learn 1 ⁨1⁩ minute 250% ⁨4⁩ seconds
2021-07-03 @ 04:35 Learn 1 ⁨1⁩ minute 250% ⁨2⁩ seconds
2021-07-03 @ 04:31 Learn 1 ⁨1⁩ minute 250% ⁨9⁩ seconds
2021-07-03 @ 04:08 Learn 1 ⁨1⁩ minute ⁨24⁩ seconds
2021-07-03 @ 04:06 Learn 1 ⁨1⁩ minute ⁨6⁩ seconds
2021-07-03 @ 04:03 Learn 1 ⁨1⁩ minute ⁨36⁩ seconds
2021-06-29 @ 22:36 Learn 1 ⁨1⁩ minute ⁨41⁩ seconds
2021-06-27 @ 08:05 Learn 3 ⁨10⁩ minutes ⁨1⁩ minute

===

This card’s “due” column just says “New #7904156”, and it has not appeared in my learning or review for months (even when the app says the deck is fully studied).

Note: I enabled scheduler 2.1 a few days ago, but the problem has been occurring for at least a month or two by now.

I think I fixed it by repositioning the cards. But I still curious how to avoid such things from happening in the future, so I wonder if there’s something I might have done to cause it…

You can fix the card added date issue with Fix invalid card IDs - AnkiWeb

For the other issue, please follow the steps on When problems occur - Frequently Asked Questions