How often is this happening?

This is the only report I am aware of. The user said he is getting notifications several times an hour. I can get more details if needed.

User says he received a total of ~30 notifications. Some arrived quickly after another, and some where several minutes apart.

Two Polish Wikipedia users reported that they receive the same notifications day after day about events that happened years ago. One user reports continuous notifications about the last edit on his talk page (message notification).

https://pl.wikipedia.org/wiki/Wikipedia:Kawiarenka/Kwestie_techniczne#Dziwne_wzmiankowanie

Adding Alex Monk, who is listed as the maintainer of Notifications.

Notifications are sent out through a set of jobs created by includes/jobs/NotificationJob.php so if I wanted to make an uneducated guess, I would suspect that some jobs were stuck in the queue somehow. For notifications about recent events (such as the fawiki issue described in the task) it is not too surprising; the job is new enough to still be in the queue so a queue maintenance error can have such a side effect. But receiving notifications about events from years ago is concerning; those jobs should be "done" many years ago and MW's job factory should have no reason to process them again.

There is an user from the Finnish WIkipedia who said that they got mentioned 5 days in a row on Polish Wikipedia:
https://fi.wikipedia.org/w/index.php?title=Wikipedia:Kahvihuone_(tekniikka)&oldid=19041003#Kerran_vuorokaudessa_toistuva_h%C3%A4lytysilmoitus_plwikist%C3%A4

@Tufor @Stryn the "X days in a row" issue is T257766: Notification emails repeated every day (which might be the same issue, but more likely isn't).

Today a dewiki user complained about recurring notifications which seem to be triggered by a 2008 (!) edit ( https://pl.wikipedia.org/w/index.php?title=Wikipedysta:JD&oldid=prev&diff=15025515 ) on plwiki, rf. https://de.wikipedia.org/w/index.php?title=Wikipedia:Fragen_zur_Wikipedia&oldid=201911169#Fehlerhafte_Benachrichtigungen and his screenshot https://de.wikipedia.org/wiki/Datei:Pl.wp.nerv.jpg . Might be the same issue?

On fawiki, User:Telluride moved a page (here) and mentioned User:Amir smt in the edit summary; consequently, Amir smt received a notification.

Apparently that page move happened in May, so this might well be the same as T257766; the only difference is that here, the notifications were sent more rapdily.

This also means the issue is not jobqueue related.

The page was edited around the time the issue happened (the first edit to it since the page move) so presumably that's what triggered it. Maybe the revision to check for mentions in the edit summary was misidentified? (Due to the newer revision not being visible due to replication lag?) Doesn't explain why it was sent repeatedly, though.

Seems different after all: T257766: Notification emails repeated every day is about old edits which are the last edit on the given page, starting to send notifications (mention or talkpage message notifications, specifically) for not apparent reason. This task is about a series of notifications being sent out for the previous edit to the page, when it got edited again.

So far, this has happened to a single user a single time, and it stopped happening. I think we can ignore it assuming it does not reoccur.

Agreed. For now let's just focus on T257766. If they happen to be the same issue, solving that will solve this. Otherwise, given that this has not recurred, we can leave it alone for now.

For both cases below there is evidence in db of repeated notifications, and, surprisingly, the same type of notifications- mention-summary notification:

In T257714#6298498, @Huji wrote:

User says he received a total of ~30 notifications. Some arrived quickly after another, and some where several minutes apart.

Checking db - for mention-summary notification 24 notifications received from the same user in 4 hours.

In T257714#6310034, @MBq wrote:

Today a dewiki user complained about recurring notifications which seem to be triggered by a 2008 (!) edit ( https://pl.wikipedia.org/w/index.php?title=Wikipedysta:JD&oldid=prev&diff=15025515 ) on plwiki, rf. https://de.wikipedia.org/w/index.php?title=Wikipedia:Fragen_zur_Wikipedia&oldid=201911169#Fehlerhafte_Benachrichtigungen and his screenshot https://de.wikipedia.org/wiki/Datei:Pl.wp.nerv.jpg . Might be the same issue?

13 notifications in this case, 7 of them were sent in 4min.
I tried to reproduce the issue - moving a page, edit an old page and adding mention in the summary in betalabs - so far, no luck for seeing the issue.

Thanks Elena!

Of note, the fawiki user said he started receiving repetitive notifications for another edit on the same page today. He also said that when he edited the page, the notifications stop. He sees "editing the page" as a temporary solution for stopping the annoying notifications.

I have the same problem that @ 1997kB has. Same edit, usually 12-20 times. Cheers!

In T257714#6317246, @1997kB wrote:

On English Wikipedia, same notification 16 times.

That does not seems like the same notification; that looks like 16 distinct notifications. Look carefully at the last words of the second line of text in each notification.

In T257714#6317333, @Huji wrote:

In T257714#6317246, @1997kB wrote:

On English Wikipedia, same notification 16 times.

That does not seems like the same notification; that looks like 16 distinct notifications. Look carefully at the last words of the second line of text in each notification.

These are 3 notifications repeating 16 times, so have total 48.

Makes much more sense.