So, after pausing a lot of times while watching because it all was so fast, there's only one thing I noticed:
You saved the root template into a subdirectory 'RootTemplate'. The root templates I created in my mod are all stored inside a subdirectory 'RootTemplates' (with an 's' at the end).
Since I never found any hint where the game might take its directories from, I assume they are hardcoded.

Although I do not know how the editor works internally, I can only assume that you find your root template immediately after you create it because it's not read from the disk but because it's still in some cache, but when you restart the editor, it will look for root templates in the folder with the 's' at the end, which does not exist and so no .lsb file with root templates can be loaded.
That's the only thing I could think of.

Try renaming the directory from 'RootTemplate' to 'RootTemplates' and see if it works.
Other than that, everything else looks okay to me.
If this is not the cause, someone else might have a hint ...