Why would bookmarks disappear? (particular ones, repeatedly?)
This kind of info should be provided when you try to create a new thread. Providing more info will really help with support and troubleshooting.
I believe the bookmarks disappear because in new tab when you can see the boxes where the last visit places if you click to high you will remove the bookmark without knowing so, idk why is done like that but after removing 3 bookmarks every time i see that i have to be very careful. They are some bookmarks that cannot be set up as well like for example: https://web.whatsapp.com/ and you cannot set shortcuts on new tab just most visited places. The visited places boxes are a nice touch but i hardly press them because they tend to remove bookmarks by mistake.