I have only one scheduled backup. This is a Full backup which runs once a week onto a NAS. This has run well for years.

In June it started running the schedule twice; the second starting a few seconds after the first has finished. It was just occasionally at first and then every week.I have tried a number of changes. The most drastic of which was to delete the schedule and all the extant backup copies and clear the NAS recycle bin. I then created a new schedule running on a different day at a different time. This ran correctly just once at the correct time last week. Cracked it, I thought. But today it has run this new schedule twice.

I have read a number of the threads and also wandered around Google. I have seen some similar problems reported but not quite the same and most seem to relate to when Reflect was using the Windows Task Scheduler which I don't think my version does (v7.3, Windows 10).

Any thoughts as to how to stop this happening would be gratefully received.

The task scheduler used is NOT dependent on the version of Reflect.  I use the latest version of Reflect but still use the Windows Task Scheduler - NOT the Macrium task scheduler.  Please check by going to the Other Tasks tab, select Edit Defaults and Settings and select the Schedule Settings tab along the top.  The first option lets you select which task scheduler to use.  If it is the Windows Task Scheduler you may have to look at the entry using the Win Task Scheduler program to see what might be causing your issue. 

Thank you. I was not aware of that. I am currently running a backup overnight - the unexpected second backup caused the NAS to run out of space so it ultimately failed and also purged the first backup! So I have started again. I will check the settings tomorrow when I can access the menu.

I had this behavior back with Reflect 7.2 when I was using Windows Task Scheduler, because that was all that was available back then.  In short, I had a schedule for monthly Fulls on the first day of each month, and what happened was that the schedule would run as expected, but would ALSO fire on the day before, i.e. the last day of the previous month.  I changed that schedule to execute on the first Sunday of the month, and once again, it executed as expected AND on the day before the expected day.

In my case, switching to Macrium Task Scheduler when it became available starting with Reflect 7.3 immediately resolved the issue.  I didn't even need to recreate my schedules.  And I haven't had problems like that since then.

Others who have previously reported scheduling problems with Windows Task Scheduler related to transitions into and out of DST, such as all post-transition scheduled executions running at the wrong time or failing to run entirely, have found that switching to Macrium Task Scheduler resolved those issues too.  I didn't have that problem with Reflect, but I did once support a client that used a different backup solution, and I found that its scheduled executions would all fail after a DST transition until its services were restarted.

Evidently scheduling engines can be tricky to write.  And I guess in some ways that makes sense.  Our calendar system is an utter mess from an engineer's perspective, with different months having different numbers of days, time zones, DST in some locations but not others (and DST transitions occurring at different points in the year for different locations), leap years that change the number of days in February and that themselves have convoluted logic to determine which years are leap years at all, and even leap SECONDS.  That's why when I participated in a beta test of the Macrium Task Scheduler engine prior to its release in Reflect 7.3, I subjected it to all sorts of bizarre scenarios to try to break it.  I found a variety of issues, some of which might never have been encountered in the real world, but Macrium fixed every last one of them prior to releasing Reflect 7.3, and I've seen little to no fixes related to Macrium Task Scheduler in the release notes of Reflect since then.

Thank you both. I have now been able to check and I can confirm that it is running on the Macrium Task Scheduler and not the Windows Task Scheduler. I have also looked at the Windows task scheduler app in case it was in both and there do not appear to be any Macrium related scheduled tasks listed as far as I can tell.

In that case, if Macrium doesn’t respond here soon, you may want to submit a formal support ticket. They will be able to request the log files from the scheduler engine itself, which will hopefully lead to identifying the underlying cause. And if it turns out to be a bug rather than some quirk of your setup, then Macrium is typically very good about promptly releasing a patch to fix it, in which case you would have just potentially saved others from experiencing the same issue.

No response so far and I do not have any current support so cannot submit a ticket. Will probably upgrade to V8 and see if that solves the issue and, failing that, will raise a ticket.

Sorry to hear that. I suppose in the meantime you could try switching to Windows Task Scheduler.  My experience and that of others has been that task scheduling issues if they exist are usually solved going in the other direction, but it would at least change a relevant variable rather than leaving you to simply continue putting up with this.

Good thought. I'll try that. Thanks.

Update:

I switched to Windows scheduling. The first week did not run - I think my fault; the second week I had significant computer issues so it did not run! Hence apologies for the late update.

Anyway, yesterday it ran and there was no duplicate.So, touch wood, problem solved. Many thanks for your suggestions and help.