How could I prevent Scrivener to always let the icons disappear:
If you use Tools > Save and Rebuild Search Engines, does that fix the issue?
What about resetting the UI? Close your project before doing this. Then in File Explorer, navigate into your project folder, then the Settings folder and delete the ‘ui.ini’ file. This will return your project to a factory default state in terms of visual and workflow settings (but won’t touch your data).
No, it does not. What does the search index have to do with the icons? Why does it make a back up when pressing that item:
After closing and starting Scrivener the symbols are available again. But I would not like to alsways restart all of the Scrivener instances each time.