Texts not appearing after upgrading

I have a project I developed in version 1.9 on Windows. I upgraded the software to 3, and opened the project (which performed a backup). All the structures and labels in the Binder are as before, but the text content of the individual files are not showing in the editor. I checked that “Scrivener.scriv\Files\Docs” (both the new one and the backup one) has kept the original .rtf files with the formatted texts. I restarted the software and reopened the project (which performed another backup), and the text files still seem “offline”, the editor is completely empty with “No Style”. Everytime I open the project, the software identifies it as “older format” despite the previous opening and conversion. During the first opening and conversion, there was some error message, but it disappeared by itself when the window loaded the project, and that message no longer comes up.

How do I get the texts back in the editor?

This sounds like some other reports, where the solution appeared to be an issue with anti-virus software. Take a look here, for example:
https://forum.literatureandlatte.com/t/upgraded-to-3-0-for-windows-text-gone/95128/1
https://forum.literatureandlatte.com/t/contents-of-texts-and-folders-are-missing-blank/95499/1

Temporarily disabling the anti-virus software (Avast, in my case) and re-installing Scrivener 3 solved my problem. Thank you very much.