I too have finally solved the problem. It was in part my own naivety in seeking access to the loader program. It was the wording on the Microsoft Store page which threw me, as it is clearly directed to those (the majority I guess) who have downloaded the app rather than purchase the 10 disks. So, having reloaded the content of the disks I was able to press ‘Install’ and after watching the download of 76Gb of necessary updates I was able to discover that the stutter has disappeared. Brill !!
Between us (Guy7001 and self) we got there but we’ve still not discovered what prompted the stutter in the first place. It’s a pity that such problems have to be solved by a hit and miss process.