Manually started backup, as seen by the varying times? 1 day interval is 24 hours (a.k.a. 86400 seconds).
You can see your job logs to get approximate backup times. Job less than 1 day after previous is deleted, however backup just completed is exempt from immediate deletion even if it got too close to the previous.
If you do manual start, is there a reason you request thinning to one per day? Just start it only once a day. You can change the 1D to U and have no limit, or you can say hours with h to whatever density you prefer.
There is a wish to allow time tolerance for scheduled backups that are a bit off, but manual is too variable.
The backup runs automatically at 7 am. But normally I switch on the pc between 8 and 10 am. That means the backup is runnig after starting the pc (thats what I want).
When I look to the time stamps of the logs I see that the backup the day before was after 9 am and the missing backup starts at 8:xx am.
I changed 4W:1D,3M:1W,3Y:1M -> 4W:U,3M:1W,3Y:1M and hope that now no backup will be deleted before 4 weeks.