I am using Thunderbird Version 78.7.1 as an email client on a Windows 10 Version 2004 PC. Since it updated Thunderbird a week or so ago I have a problem with the built in calendar and so far I cannot find a solution for it.
I have several events that repeat ever month or possibly every 4 weeks in some cases. Occasionally I need to alter just one instance of the event, for example moving it from a Saturday/Sunday to the preceding Friday. Whenever you edit an event it gives you the option of changing just that instance of the event or all instances of that even going forward. This worked up to the latest update but no longer does. If you edit just one event it changes on the calendar but if you close Thunderbird and open it again it reverts to its original date in the sequence.
Is anybody else experiencing this problem and, more importantly has anybody found a solution. I have tried searching the internet but don't seem to be able to find this specific problem