Sorry, LUD-16 (standard for implementing lightning addresses)

They get stuck by constantly trying to find a route, and it keeps failing. If you close the sending and/or receiving wallets, those funds could be identified as "spent" when you reopen, or on the other end, "still pending" and not received.

If the app stays open, the payment just times out and records that failed payment.

Never close your lightning wallet when sending a payment. Or receiving one.