I followed the solution posted by "Richard & Janet Myers - 8/11/25, 1:46 PM" and it appears to have worked for my events. I do not have any tasks and only a single calendar.

I opened Thunderbird Settings, went to the Calendar Settings and scrolled down to the Reminders section. I then clicked the <Show missed reminders for writable calendars> check box. I then dropped down to the Notifications section. The only one listed was the <1 minute before the event starts> that I've been using for years. As soon as I clicked the [ + Add notification] button, the second notification of "0 minutes before..." appeared and so did a pop up listing the 13 missed reminders dating back to July 21st, when it stopped working reliably. The last of those 13 is a future event with a Reminder set for 21 days before the event starts. Today's repeating Monday reminder popped up like it always used to.

For any others experiencing issues with missing Task (not Event) reminders. I've found that mine show up in the pop-up notification window as long as Thunderbird is open at the time the alert is set to pop. Unfortunately I have most of mine set for before I start my day on the computer and they have not been showing up. They also don't show up again once you close the pop-up window, even if you haven't dismissed them.

I've opened a bug report. I'll post any results when I hear back. Meanwhile if anyone wants to follow its progress it can be found at https://bugzilla.mozilla.org/show_bug.cgi?id=1984129

Same issue here. Tried all proposed solutions and workarounds listed here and at other places. None work for me with reminders for Tasks.

To me it seems as if the "Show missed reminders for writable calendars" option simply does not apply to Tasks but only to regular calendar entries. Not sure if that was/is by design. But I would very much need some option that enables this for Tasks as well.

@Mike00 would it be ok to link your bug report here? I did find it but I am just not sure if linking it here is appropriate.

Same issue here. Tried all proposed solutions and workarounds listed here and at other places. None work for me with reminders for Tasks. To me it seems as if the "Show missed reminders for writable calendars" option simply does not apply to Tasks but only to regular calendar entries. Not sure if that was/is by design. But I would very much need some option that enables this for Tasks as well. @Mike00 would it be ok to link your bug report here? I did find it but I am just not sure if linking it here is appropriate.

I felt the same way about that option but the person who received my bug report modified it in such a way that makes it seem like it was supposed apply to tasks as well. We'll see what happens I guess.

Per your request I added a link to the bug report in my original post.

Had the same problem as noted by "wlcws1" above and followed those directions and all my missing reminders showed up on screen. Thanks wlcws1.....

I don't like to tempt fate but having had the same problem of no reminders for a few weeks now, tried all suggestions from other threads on the same problem to no avail, or at least only temporarily One reminder would come up every day (a recently set one) but others didn't (I have several set for daily or weekly or bi-weekly and random ones) One or two would appear then disappear without my intervention But today, out of the blue all my missed and missing reminders popped up, so having now caught up with the backlog I am hoping its been fixed, time will tell We can only hope

Well my hope evaporated the next day, I am getting the weekly, monthly and yearly reminders but daily ones come and go with no obvious pattern, I can make them appear by editing each reminder, and just selecting save without changing anything, up pop all previous reminders for that task (I say task as thats what its called "New Task", I only have one calendar but only ever add reminders under "New Task", so an unsure what the difference is between "Task" & "Event") I have one daily one that comes up every day, but others do not, I can see no obvious difference between them

I basically only use Tasks to get reminders, so as a workaround for the missing Task reminders I converted all my Tasks to Events in a new local TB calendar to keep them separate from my other calendar events, that way I can just delete the whole calendar once the Task reminder issue is fixed if I want.

Note: when the convert is done it leaves the original Task and copies it as an Event.

To do the convert open the Task tab, in the left pane select the calendar you want to place the Event in (this will autofill the Calendar field in the Event popup window), then select one or more Tasks and right-click on one to open the options pull-down list, select "Convert to">"Event". This will open a popup for each Task selected so you can modify the new Events if you want before saving them.

@Mike00: Bug has been closed as duplicate, the new link is: [https://bugzilla.mozilla.org/show_bug.cgi?id=1972904]

Could you please look something up/confirm something? I just noticed on reproducing the error that I never set any due dates for my Tasks. When I do they actually do show reminders for me. At least if I open TB while still in between start and due date. Is that the same for you?

@Mike00: Bug has been closed as duplicate, the new link is: [https://bugzilla.mozilla.org/show_bug.cgi?id=1972904] Could you please look something up/confirm something? I just noticed on reproducing the error that I never set any due dates for my Tasks. When I do they actually do show reminders for me. At least if I open TB while still in between start and due date. Is that the same for you?

Most of mine also don't have due dates set but some had due dates a week or more away and as I recall once the initial start time was missed I didn't get any reminders about it for the duration of the task but that may have been before I found out that TB changed it's default to turn off missed reminders. I have since enabled "Show missed reminders for writable calendars".

I created a short test task and closed TB before the start time and then opened it between the start and due times and I DID get a notification of the missed task. I also closed the reminder window without dismissing the task and I got a subsequent reminder about 5 minutes later which is my default snooze length.

I ran a second test tonight to see if an expired task would open a reminder window if it had start and due times with TB closed for the entire duration of the event and it did.

Lastly I tested a task with a start time but no due time. With TB closed before the start time and opened afterward there was no reminder.

I have never ticked/used Due Date (DD) in my Tasks - I had no need to for the way I use Tasks and Reminders; and no need to with previous version of Thunderbird.

Following Mike00's last helpful note, I tested ticking DD on new tasks (DD date + time = start date + time). So far, Reminders are now appearing as I would expect them to, though I am still testing all power off/on/sleep-when-reminder-due scenarios.

I have also started ticking DD on my (at least) 150 tasks, both individual and repeating. So far, so good - Reminders are appearing as expected and as they would have previously.

So for me the key so far is to tick Due Date on Tasks. I do hope this helps others.

It looks like there's a fix in the works for the missing Task alert issue. The bug report I opened, Bug 1984129 and the one that it was moved to, Bug 1972904, have both been closed. I don't know when we'll see it but there is a code fix being reviewed.