I sent a Lightning transaction but it wasn't received (see Strike & Muun)

As explained in other articles, sending and receiving Lightning transactions is done using submarine swaps from/to Layer 2 Bitcoin (L-BTC).

These trustless swaps are carried out via Boltz in the backend, and while the vast majority of AQUA Lightning transactions will be successful, some issues can arise (see errors receiving Lightning in AQUA). As of now, sending a Lightning transaction to a Strike account can cause the transaction to show as if it has failed, whereas in reality, the funds have been successfully received by Strike. This a known issue for the AQUA, Boltz, and Strike teams, and it’s currently being worked on.

Similarly, Lightning payments to Muun Wallet (which also uses submarine swaps, albeit with on-chain Bitcoin) have been known to be affected by excessively long delays too. AQUA and Boltz developers are also looking into this matter.