failed restores with EaseUS Backup

I am using the free edition of EaseUS ToDo Backup and run into problems with restoring in a specific situation.

I was doing regular full backups of a Win7 system partition, located on Disk 1 (not sure if it matters, but when I installed Win 7 a long time ago, I forced Windows to use that partition for all files, including the win recovery files which would be placed otherwise on a distinct recovery partition).
I transfered a backup B1 of the win 7 system to a different disk, Disk 2, and restored it to a system partition of Disk 2. All fine. Removed Disk1.
Running Win7 on Disk2, I performed un upgrade to Win10, keeping all files and applications (Win 10 now created a distinct partition to store the win recovery files). All good.
Using the exact same disk/partition mechanism, I created a backup B2 of the resulting Win10 system partition on Disk 2 and stored it (the recovery Win 10 partition not included). Actually B2 was the last backup I kept of that experiment, before B2 I also did create and restore successfuly some intermediary backups of the Win 10 system partition.
Decided to start a new upgrade experiment, started again by restoring the B1 Win7, upgraded to win 10, then created a new full backup B3 of the resulting Win10 system partition on Disk 2 and stored it.
Now I tried to restore B2 to the system partition on Disk 2, but the restore with EaseUs hung at 99 percent ("Updating system information...") and did not finish in a few hours (usualy it takes around 20 min).
Using an emergency disk, I tried to restore both B2 and B3 to the system partition on Disk 2, same hanging at 99 percent.
Now I tried to restore B1, which worked. Checked Disk 2, no problems. All was MBR, and the Disks 1 and 2 also have some additional data partitions which are also fine and were used to store backups etc.
I checked backup B1, B2, B3 using the EaseUS software, it says that all are fine. All I did in these experiments was add/remove programs to check compatibility with Win 10, everything was fine when taking the backups.

What could be the cause of not beeing able to restore backup B2 and B3?

So I backed up two different Win10 branches originating from the same Win7 starting point.
B1 = the Win 7 backup, used as a starting point
B2 = a Win10 partition backup, resulted by restoring B1, then upgrading to Win10 (keeping all apps), experimenting with drivers on win 10, then backing up the Win10 system partition
B3 = a Win10 partition backup, resulted by restoring B1, then upgrading to Win10 (keeping all apps), experimenting with drivers on win 10, then backing up the Win10 system partition

I am always able to restore the original Win7, no problem, the drive is healty (crystal disk 100 percent healty, 3 percent ssd lifetime wear, no bads), using it right now.
While working on the B2 path, I made intermediary backups of the Win10 partition as checkpoints, and I was able to restore such an intermediary backup at that time. The last backup of this path was B2.
After starting over from B1 and doing a similar experiment , I saved the last backup of this path called B3.
At this point I was unable to restore B2 (restore stuck)... used emergency disk and realized that I cannot restore neither B2 nor B3 (restore stuck).

So what I would like to know is why a backup of a system partition containing Win10 cannot be restored in some situations (see above), yet is works in particular situations (see intermediary checkpoint backups that I was able to restore, on B2 path).
Does Win 10 keep some vital info elsewhere beside the system partition? is the Win 10 recovery partition (the one having around 600MB, and with no drive letter assigned) vital? That seems the only logical explanation to me...
Also would help to know if anyone knows how to upgrade a Win 7 partition (that includes the Win7 recovery files) to Win10 so that Win10 would not put the Win10 recovery files to a new(different) partition?

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@Ghot
This has nothing to do with licensing...

Thanks for your help... this may explain it.
I was living with the idea that the System reserved is disposable and that it contains only the windows recovery files (didnt even bother to back it up). I see this is not the case ...
So the simplicity of backing up a single partition goes away after the upgrade from Win 7 to Win 10. Like I said, when I installed Win 7, I forced the installation to happen on a single partition, which was helpful with backing up/restoring.
Still need to check what happens when upgrading, but it looks like unless I find a way to convince the Windows 10 to use a single partition when upgrading, then at least 2 partitions would need to be backed up...

Oh, but there is no System Reserve in my case (which would be required), it's only the Recovery partition that got added with the upgrade. So backing up only the system partition is correct.

So the puzzle remains unsolved...

And a side note... funny how many people dislike the many partitions that windows does by default :)

Does it always stick at "updating system information" ?

The B3 and B2 backups, and also another one that I took right before B2 are all hanging when trying to restore.
Initial B1 is fine.