Thanks for your feedback. It looks like there's still several issues with the rich text editor. I'll have a look.
Are you using the Samsung default keyboard? Could you check if switching temporarily to GBoard fixes the issue where the page keeps going blank? I thought I'd fixed issues with Samsung Keyboard jumping around the scene without user input but it sounds like that could be what's happening.
Regarding the saving issues -
When the project is open, it will show the file path it is saving to at the top. (Project Title by Author (word count) [Current save file path]) Can you check that this path matches your dropbox file location.
Also, make sure that yWriter on the PC is closed while you are editing on mobile.
Local backups will also be saved on mobile in Local yWriter App Storage/AutoBackups which can be opened from mobile if you lose data.
On mobile, you can check that the Beta version has definitely been updated to the latest version by opening yWriter, clicking the 3 dots in the top right on the main page and selecting 'About/Help' - check that it says 2023.12.4.124 (latest version number) at the bottom. If it hasn't been updated, go to google play and check for app updates (Click profile -> Manage apps and devices -> Manage -> Updates available -> check for yWriter).