After having gone back through the thread, here are some ideas on the issues (in no particular order).
It would be a good idea to run chkdsk on the Windows partition before copying it to make sure it’s clean. For example, from a Windows administrator command prompt (it will likely need to reboot to check): chkdsk /f c:
Fast Startup is supposedly disabled on both systems. Make absolutely that it is because it can cause issues like what you’re having. Especially since you’re repeatedly installing/copying/configuring Windows. It would need to be checked each time.
If the system is using a separate drive (or part of a drive) as a cache that can also cause the same types of issues if it gets out of sync or corrupted. If being used, disable it. There is usually an option in the BIOS if this is a feature on the system. Some systems with Intel chipsets have this type of feature, for example.
How old is the system? Is the BIOS current (or as current as can be)? It’s mentioned at one point that there was an “Unable to open BOOTIT.DAT” error message. This can be caused by the UEFI file system not being able to be remounted. It may be that the BIOS isn’t fully supporting BIU (especially if it’s an older system).
https://www.terabyteunlimited.com/kb/kb ... r-message/
In BIU Settings, make sure the “Rename Directory” option is enabled. It should be (just checking). Also, make sure the “Use Boot Item Disk IDs” option is enabled.
Can you open “Scripting” from the BIU desktop and then run ‘exit’ to return to the desktop without getting an error message? Can this be done multiple times without issue (say, 5 times)? Same for IFU (“Disk Imaging” icon on desktop).
When Windows has an issue booting and tries repair mode (like the issue you’re having), you could use the fixboot.tbs script to repair/rebuild the boot configuration files for the Windows that has the issue and see if it helps.
In the BIU boot menu items for each Windows, you could try NOT hiding the partitions from each other. At this point, we’re just trying to remove things that may complicate the setup.
It really sounds like things are working sometimes and not sometimes. It may be that the system is borderline in supporting what BIU needs to function.