My reading list has disappeared after a few second i added website to reading list.

Note that if anything is removed from the reading list on any device, it will also be removed from the other devices.

Please disable Safari synchronization on all your devices. Arrange the reading list on the Mac as you wish. Reenable synchronization on the Mac first, then on the other devices.

If the above doesn't work, try a restart.

Do a backup, using either Time Machine or a cloning program, to ensure files/data can be recovered. Two backups are better than one.

Try setting up another admin user account to see if the same problem continues. If Back-to-My Mac is selected in System Preferences, the Guest account will not work. The intent is to see if it is specific to one account or a system wide problem. This account can be deleted later.

Isolating an issue by using another user account

Have you tried booting your computer in Safe Mode? Shut down your computer, then restart it while holding down the Shift key. This clears all system caches and disables a lot of bells and whistles in the form of add-ons — it will allow you to see if the problem is something that can be fixed by uninstalling something or if it's something wrong with the hardware/operating system. When you're in Safe Mode, open Safari. Do you see the duplicate new tab button? When you add something to your reading list, does it stay there?

Delete com.apple.Safari.plist file and test.

Empty the Trash.

Quit all applications.

Hold the option key down and click the "Go" menu in the Finder menu bar.

Select "Library" from the drop down.

Library > Preferences > com.apple.Safari.plist

Right click on it and select "Move it to Trash".

Close the Finder window.

Restart. Relaunch Safari.

If this doesn’t help, “Put Back” the com.apple.Safari.plist

Right click on the Trash icon in the Dock and select “Open”.

Right click on the com.apple.Safari.plist and select “Put Back”.

Please open the iCloud preference pane and uncheck the box marked Safari. Test. Then check the box again, if you wish. Post the results of the test.

Safari > Preferences > Extensions

Dissable all extensions and test.

Enable Extensions one by one and test.

To uninstall any extension, select it and click the “Uninstall” button.