Strange, unpredictable behaviour of unsuspended cards in AnkiDroid

Question

Could you explain me the following strange and unpredictable behaviour of unsuspended cards in AnkiDroid?

For a very long time I didn't block my "leeches", because I considered it annoying. Finaly, after many years I realised that they are actually an important part of learning. That caused that many of my flashcards have now several dozen "lapses" :D

I enabled suspending my cards and now I have several dozen suspended cards. So I unsuspended some of them, but then soming strange and unexpected happend.

The anticipated behaviour was that my unsuspended cards won't be suspended again untill I give, say, 8 false answers in a row, wasn't it? But in reality my newly unsuspended cards became suspended again after one false answer!

So I started to experiment with my suspendend cards. I took 6 flashcards to an entirly newly deck and started to review them with a filtered deck. The results of my experiments are as follow:

1. When the limit of leeches was set to 1,2 or 3 lapses the flashcards became suspended after 1 false answer. They should obviously become blocked when the limit was 1. But why did they became blocked when te limit was>1?
2. When the limit was set to 4 or more (I experimented with 4, 8 and 16) the flashcards didn't became suspended after 1 or 2 false answers.
3. I experimented with different language set in my Anki but it seems it doesn't matter.

I tought for a while that I had found the explanation of such strange behaviour. AnkiDroid remembers the number of lapses for every flashcards. Let's denot it by L. Let's denote the limit of lapses by Limit (for instance Limit=8). I suspect that AnkiDroid suspends a flashcard when

L/Limit=a whole number.

Thus a flashcards (given the limit 8) would be suspended for the first time when L=8, for the second time when L=16 and so on so on.

So I thought that maybe the numbers of lapses of my selected flashcards (L+1 to be more accurate) where divisable by 1,2 and 3 and that's why they are suspended when Limit=1,2, or 3, because (L+1)/Limit=a whole number.

But I checked their numbers of lapses and they were as follows: 16, 24, 32, 16, 24, 48. Hence after one false answer they were 17,25,33,17,25,49. And 17, 25, and 49 aren't divisable by 3. So what the flashcards were suspended when Limit=3? On the other hand none of these numbers is divisable by 2, so none of the flashcards should have been suspended after 1 false answer when the Limit=2.

If the above is not enough I could swear that my unsuspended flashcards got suspended after 1 false answer also when the Limit=16 (at least some of them) :(

So, in a nutshel I have no idea how AnkiDroid is working on this matter and hence don't know what to do with my suspended flashcards :( And it's a problem, because I have more and more of them.

Could you help me? Could you explain to me such unpredictable behaviour? Is it a known bug or what?

Answer 1

Anki will continue to issue leech warnings periodically for a difficult card. The warning interval is half the initial leech threshold. That is, if you have Anki configured to warn at 8 lapses, future warnings will happen every 4 lapses. (12, 16, etc)

This is taken from the official Anki manual. Ankidroid usually achieves to follow these specifications, and it matches your observations: 16, 24, 32, 16, 24, 48 all satisfy 16 + 8x.