This seems to be a fairly common problem with the Jaxx wallet... for whatever reason it sounds like their server keeps doing weird things and users have to "reset the Jaxx cache" all the time to see their transactions and coins
Although, I'm wondering if this is a case of someone sent your coins, and the wallet was showing you the "unconfirmed" transaction... but then the transaction was either dropped or double spent and so Jaxx removed it from your wallet as it no longer existed.
Do you have any records of the transaction (like the transactionID) which you can lookup the transaction on a block explorer like blockchain.info etc? or the address that the coins were supposedly sent to?