Rise files have disappeared after moving to new folder (and then deleting old folder)

My Rise files have disappeared. Here is the context:

We had to transfer ownership of Rise course files from a colleague (let's call him X) to me because X is retiring. 

When I realized that X still owned the main folder that the files were in, and because there does not seem to be any way to transfer ownership of Rise folders, I created a new main folder and transferred all the sub-folders from the old main folder into the new main folder. 

(I am not comfortable with someone no longer with the company owning folders, which is why I wanted to be the folder owner.)

Both main folders are in the Team section of the Rise 360 content "menu".

When I looked at the old main folder, after having moved all the sub-folders, it was completely empty of sub-folders. I then told X that he could delete the old main folder via email.

Just after that, I realized that all the sub-folders in the new main folder also belonged to X. I then emailed X to tell him to hold off deleting the old main folder, because I wanted to transfer the course files into new sub-folders that I was in the midst of creating in the new main folder.

(I was going to move the empty old sub-folders back into the old main folder once I'd moved all the course files, so that X could delete all the empty folders at once.)  

Suddenly, all the sub-folders that had been transferred into the new main folder from the old main folder disappeared. I suspect they disappeared when X deleted the old main folder... even though they were no longer IN that old main folder (as far as I could see). X had not gotten my second email at that point. 

I contacted X, and he restored the old main folder and the sub-folders - which he said had still been visible when he deleted the old main folder. As I said, this was not what I had seen. On my system, the old main folder was completely empty. 

And ... when X restored the old main folder AND its sub-folders... the sub-folders were empty.

We cannot find the course files. 

• X did not permanently delete the course files.
• They are not in the Delete folders on either of our systems. 
• They are not visible when viewing All Content on either of our systems.
• We do not know where else to look. 

Obviously we need help!