Some cryptocurrencies, especially Bitcoin, have a lot of activity happening on its blockchain network.
If you notice that you are receiving back the digital assets that you're trying to send, it could be because of a congested blockchain network for that particular coin / token.
This would often occur when the selling price for a certain cryptocurrency is high because of the high amount of traffic within the network.
Unfortunately, the blockchain congestion and speed of transactions is not something that we can control.