I generally do not reply to mac users. I do not pay the apple tax and don't intend to, so I have no idea what the interface looks like or the general menu commands.

But you have now posted three times to this forum, in none of the posts have you actually offered diagnostic information on which someone might be able to comment. We know exactly what you tell us, nothing more.

Apparently you are "loosing" entries from your calendar. I am not aware of a single other post with than complaint. Although only a few percent of users are currently on V102. It was released for "automatic upgrade" only in the past few days. So all the existing users are supposed to be early adopters that downloaded the new version or new users.

Is it a local calendar, on a network or something else. Most folk have shared calendars from google, yahoo, GMX etc. If you are not doing that it is important to explain your setup.

Is your calendar supplied by an addon to implement exchange server, or perhaps the provider for google calendar?

A good starting point might be to post the more troubleshooting information on the help menu. (copy to clipboard and paste into a reply on this forum.)

Is your profile in a default location? Remote storage is not supported, and while folk love to put things on NAS devices, or cloud synced locations these are quite prone to profile corruption.

You have a backup I see, is it of the streaming kind? These can cause all sorts of issues if they attempt to backup files while they are being used.

Do you have an antivirus program? if so have you excluded the Thunderbird profile folder from on access scanning? again, like streaming backup and cloud syncing. File contention often causes issues.

If you'd had my experiences with Windows ME and then had to put up with the constant Windows errors in subsequent Windows additions (pre Windows 10) you'd have paid the Apple tax, and glad of it! When I bought my first iMac MacOS was vastly superior to Windows (it was like night and day). However, since the advent of Windows 10 (haven't yet tried Windows 11 because my laptop isn't compatible) I would agree that Windows is as good as MacOS and I'm pretty tired of my iMac getting slower and slower with each successive MacOS (the built-in Apple redundancy that makes your Mac "obsolete" within seven years). I would consider going back to a Windows desktop PC but I haven't yet found one with the same aesthetic appeal of a 27" iMac. My bad.

This is the third time that I've posted and the first time I've had a response!

I apologise if I've previously misspelt losing; I appreciate how critical spelling is to diagnosing the problem!

I have no diagnostics to offer because, to all intents and purposes, Thunderbird seems to be working okay (it's not crashing). In answer to your other questions:

- my problems started with the Thunderbird 101 upgrade (and continues with Thunderbird 102); - it's a local calendar on my iMac; - I don't use shared calendars (I only access the calendar on my iMac); - I use the integrated calendar in Thunderbird (I removed the Lightening add-on when it was integrated); - my profile and calendar data are in the default locations; - I use Time Machine to back up my data (I've had no problems pre Thunderbird 101); and - I use Intego anti-virus (this did not give me any problems pre Thunderbird 101)

I've been using Thunderbird for over ten years and the calendar for over 5 years without any issues.

The problem I have is most unusual. When I upgraded to Thunderbird 101 I noticed that some of my existing calendar events appeared to have visually disappeared. I initially thought it was my imagination but over the next few days a lot more events visually disappeared (not all, but most and there did not appear to be any discernible pattern - some months would be completely empty whereas other months would have a couple of entries) and I couldn't add any new events (I'd enter them but they would not appear to the visible eye). I say visually because I was still getting (at least) some reminders when I opened Thunderbird despite the events in question not being visible in my calendar. So, I know some of my missing events are still there despite not being visible but I can't say whether that's true of all my missing events (I am unable to discern whether my missing events are simply not visible or whether some missing events have been lost completley).

So yesterday, I decided to delete my old calendar, create a new blank calendar and re-key in all of my events from scratch. Everything seemed to be going okay (I was able to enter repeat events with reminders, such as birthdays, without any apparent issue) until I entered an event that I wanted to repeat on the last day of every month. The first time I tried to enter the event it didn't appear. I thought I mustn't have saved it, so I entered it a second time. I then moved to the next month to check that the repeat had worked and noticed that some of the events that I'd previously entered had again visually disappeared and when I returned to the previous month the new event had also visually disappeared and, on further investigation, I noticed that yet more events had visually disappeared.

In the end I deleted the new calendar in frustration (in part due to having then read that the calendar function is no longer being supported by Moz://a) and downloaded BusyCal instead. I now plan to give that a trial. At first glance it's not as good as Thunderbird's calendar but at least it appears to be bug free.

I apologise in advance for my British spelling and any other unintentional typos ;-)

I have no idea where you get the idea the calendar (which is an integrated component of Thunderbird) is not supported. It is as supported as any other part of Thunderbird. The "backlog" of work publish on the roadmap includes 15 fairly significant calendar enhancements, including what almost amount to a rewrite. https://developer.thunderbird.net/planning/backlog

As for Mozilla, they started their withdraw back in 2012. https://blog.lizardwrangler.com/2012/07/06/thunderbird-stability-and-community-innovation/ About a year ago they created a new for profit company that could "hire" the folk working on Thunderbird and paid from the donations the project receives. While this forum and the bug system along with some other components use Mozilla infrastructure. The management and the funding of the project is completely separate from Mozilla and has been for most of the last decade. If you look at the Mozilla foundation web site you will not see Thunderbird listed as on3 of their products.

As for spelling, I have to install a US dictionary so I can abide by the EN_US policy of project language that we inherited from Mozilla. I speak strine.

I would actually like to see an ICS file exported from Thunderbird for this calendar. (it is on the Events and tasks menu) You say things are missing, seeing what is exported may provide some sort of a clue. I assume you can restore your calendar from time machine. Just because you can't see things does not mean they are not there.

Personally I use online calendars network linked to Thunderbird, primarily Google. That way I can use the same on my phone. It also help to sync contacts between the phone and Thunderbird via Google and Google will automatically populate a birthdays calendar with contacts birthdays.

I didn't say the integrated calendar wasn't supported; I said it wasn't supported by Mozilla (it, like Thunderbird, is supported by the community).

I accept that just because I can't see things doesn't mean that they are not there BUT they are not much use if you can't see them ;-)

To export the ICS file I will need to copy the data files from Time Machine (as you suggest). Can you please advise which data files I'd need to overwrite from my Time Machine back up so as to reinstall the calendar I deleted. prefs.js? storage.sdb? storage.sqlite? A N Other file? Thanks

I only use the calendar on my iMac and don't need to sync it with any other devices (I try to avoid using the Cloud as little as possible; Big Brother issues)