Old, already read notifications appear as unread at unrefreshed tabs

[kukutz]

1. Any OS and browser, mobile (reproduces more often) and desktop.
2. Main frontend
   3.1. Open freefeed.
   3.2. Leave tab for some time as non-active, use another tabs.
   3.3. Receive some notifications.
   3.4. Send device to sleep.
   3.5. Read notifications on another device.
   3.6. Switch on first device and activate old freefeed tab.
3. What actually happens: tab contains unread notifications which were read on step 3.5.
4. What should happen: I think we should detect "back to online" situation and refresh notifications counter at step 3.6.