If you're chatting to your Connections and notice that your messages disappear after sending, you can fix the problem by killing the app and logging in again.
If on iOS, you can follow these specific steps:
1.) Double-click on the Home button to bring up the 'fast app switcher'.
2.) Swipe up on the Feeld card by flicking it up and off the screen.
3.) Tap the Home button again to return to the main screen.
4.) Tap on the Feeld icon to reopen the app.
5.) Try sending your message again.