TOC "hides" all but the first book in Responsive HTML5 output on smaller screens

Adobe Support advised me that, because I had to manually recreate so much of the TOC (because our project was so disorganized), it "rebroke." A little history of the project: it was created with no logical folder structure in Contents, and a former colleague subsequently lost the project and then "recreated" it by importing the Responsive HTML5 output back into RH. We have had many random issues with the project since. Adobe support had told me to delete a bunch of JS files to attempt to fix the corruption introduced by this "recreation." So, yesterday, to attempt to fix the TOC issue and possibly leave us with a corruption-free project, I created a brand-new project, and am creating logical folders into which I'm importing topics from the "recreated" project and relinking the style sheet and images. So far, as I'm testing by auto-generating the TOC, the TOC issue is not recurring. Peter, in your opinion, is this method of recreating the project likely to retain any of the corruption introduced when my colleague imported the output files? How would you advise me to proceed? Thank you!

Actually, that didn't work: the issue seems to be intermittant. I opened a ticket with Adobe Support. The support rep advised me the TOC file was likely corrupted when the project was upgraded from 2019 Classic RH to the new interface, and that I should delete the TOC and create a new one. That seemed to work, but again, only intermittantly: as I continued to add new "books" to the TOC and generate the output, the issue reoccurred.