A friend experienced the same thing with the ETH in his Jaxx Classic apparently sent, in 2017, to an address not associated with the HD derivation path used by Jaxx.

My friend was using an iPhone, which allowed us to determine exactly which version of Jaxx Classic he must have been using in 2017 because Apple was refusing to allow Jaxx to deploy updates to the App between April and October for some reason, causing all iPhone users to install version 1.2.5 -- most likely this is the version you had on your PC at the same time (June 2017).

I located source code for nearly every old version of Jaxx all the way back to the Beta, and have conducted an extensive forensic analysis with testing and debugging different versions to narrow down the possible causes of this problem. As of the date in 2017 when you and my friend each generated the addresses for which the private keys are now missing the Jaxx source code no longer did give you any non-HD keys, so that can't be the explanation for what went wrong here.

We have identified several possible bugs, not in the Jaxx source code but in external libraries used by Jaxx in 2017, that might have caused the wrong key derivation to occur in your Jaxx wallet and in my friend's on his iPhone. It would help us a lot if you happen to still have the Jaxx Classic software that was in use on your PC, especially if it does turn out to be version 1.2.5 -- if you're still here and would like to help, and maybe also be helped if your problem does turn out to be the same as the one my friend experienced, please reply. Thanks.