Your transactions can get dropped from the memory pool if there is a lot of congestion on the blockchain network. When a transaction gets dropped from the "mempool", the funds will be refunded to the originating address. I.e if you transacted BTC from your Jaxx wallet to another wallet and it fails, your funds will return to your Jaxx wallet.
Your transactions could fail due to other reasons:
1. You have firewall, Tor or VPN enabled. These services may interrupt information from being relayed to the blockchain. Please try disabling them and try again.
2. You are not connected to a strong WiFi network. If you're on a public network or a restricted wireless network (WiFi at work, WiFi in public, etc.), you may need to switch to a stronger, private network or your cellular data.
3. You reached the maximum deposit limit (for ShapeShift transactions). If your ShapeShift transactions are failing, you may have exceeded your deposit limit for the day.
In the case of your transaction getting dropped from the mempool, you can identify that this is the case by checking the clicking on the transaction hash found under the Transaction ID in your Transaction History to see whether the transaction exists on a block explorer. If the transaction hash cannot be found, your transaction likely got dropped from the mempool:
1. Please Reset Jaxx Cache if your transaction is still recorded in the Transaction History in order to bring the funds back. Please make sure you have your 12-word Backup Phrase written down prior to doing so. If your transaction is still recorded and your funds haven't returned to you, your transaction may be in queue to be picked up by miners.
Please keep in mind that it does take up to 72 hours for your transaction to be fully dropped from the mempool.
2. You can always check whether your transaction has gone through or not by copying and pasting the public address you sent your funds from on a block explorer to verify whether your funds have been withdrawn from your wallet.
3. Please try and pair to another platform to see whether this is a cross-platform issue.