Obtaining 12 word mnemonic from Private & Public Keys After a recent upgrade to Jaxx wallet my Litecoins and my transaction history are lost. 

The 12 word mnemonic opens up a wallet with zero Litecoin balance even though the public key address from the earlier Jaxx wallet shows the coins are available and unspent on blockchain.My mnemonic seed has not changed yet Jaxx wallet is not the same.So apparently there may have been a bug in the seed derivation path or ......

Jaxx support is not able to help and they say I am not using the correct mnemonic. This is not at all possible. Unfortunately I do not have the private key for the public key address where my coins are as Jaxx wallet no longer shows me the same set of earlier public/private keys and transaction. 

For most of my earlier transaction I have public and private key. Can I generate the 12 word mnemonic from the set of private/public keys just to confirm?
Sorry you can't invert a private key from a detached BIP 44 path to obtain a BIP 39 seed words. That is the mathematical nature of BIP 39 when combined with BIP 44.  However, Electrum seed words used by Monero are invertible from a Monero private key.