I have a set beatmapsets/2331746 which should have ~7 difficulties since last update (8 days ago), and I'm pretty sure it's the case even until yesterday. But when I check it today, somehow only 3 difficulties are shown.

The map is submitted from lazer, if that's relevant.

Can you export the beatmap (from lazer) and it through a file/media sharing website for us to take a look at, and once done can you attach the link to a new reply, make sure that its viewable to all who have the link.

The beatmap export is not necessary. The online .osz has 7 .osu files inside. Something is clearly wrong.

The four difficulties in question appear to have been deleted on 2025-05-27 12:53:47 UTC. We've restored them for you, but this doesn't really explain why this happened.

@OP:

1. Are you sure you did not attempt to update the beatmap within the last day?
2. Are you sure you didn't get any submission errors at any point?
3. Please logs, button to export them is in settings.
4. I notice that on your profile page you have a section with "some lazer tweaks". Did you submit the beatmap from an unmodified and official version of the client?

I tried to recall what I did yesterday, and I think I have found out the reason.

First of all, I have an old version of this set with only 3 diffs in stable. You can it here: https://kanatama.s-ul.eu/oannnt6c
Then all other diffs except the 3 will disappear after the following steps:
1) enter the Hard diff in stable editor (idk if it has to be the Hard diff)
2) open the beatmap dialog (ctrl+shift+u)
3) when the dialog appears (you are one step away from....), click cancel.
tbh I'm very surprised that the online beatmap is still changed in some way even if it's cancelled before update...

And now when I try to the set from lazer again (on the official build), I get the error "one of the beatmaps to keep does not belong to the specified set".

regarding the questions:
1. I think I accidentally triggered the map update dialog on one map yesterday on stable (and cancelled it), and it looks that this map is the victim
2. it's a long time ago and it has been updated multiple times, so I can't recall, sorry...
3. https://kanatama.s-ul.eu/oqrmxops
4. usually I map (and submit) with my own build with those tweaks. You can say I have lost the right to ask for help by doing so, but the tweaks should not involve the beatmap submission system and I have used in this way at least since the first day of lazer submission , so I doubt that is the reason

-infinite- wrote: 1r1u6j

(...) and I think I have found out the reason.

First of all, I have an old version of this set with only 3 diffs in stable. You can it here: https://kanatama.s-ul.eu/oannnt6c
Then all other diffs except the 3 will disappear after the following steps:
1) enter the Hard diff in stable editor (idk if it has to be the Hard diff)
2) open the beatmap dialog (ctrl+shift+u)
3) when the dialog appears (you are one step away from....), click cancel.
tbh I'm very surprised that the online beatmap is still changed in some way even if it's cancelled before update...

And now when I try to the set from lazer again (on the official build), I get the error "one of the beatmaps to keep does not belong to the specified set".

(...)

1. I think I accidentally triggered the map update dialog on one map yesterday on stable (and cancelled it), and it looks that this map is the victim

That is indeed the reason. Stable submission does a preliminary online request to assign online IDs to the beatmaps being submitted, which also may delete beatmaps which are not being submitted as far as stable is concerned. This logic has been there for a long time, precedes me, and was weird enough for me to change for lazer submission - lazer beatmap submission will never do anything like that before you go through the submission wizard fully.

The deleted beatmaps have been restored for you again.

ok, thanks for the explanation (and restoring the maps).