Have you tried resetting your preferences? Have you tired other formats such as tiff? It would be better to use tiffs for the scan, if you're going to correct the image further, as that will reduce jpg artifacts.
I have the same problem. There is no 'Open As' command anymore under File in Photoshop 2015.5.0
At the moment you can only open the jpg in Photoshop and then use the 'Camera RAW filter' under Filter.
To me that's not what I need. I need to open it straight into Photoshop as I use a Guy Gowan action that needs jpegs to open in Camera RAW.
This happened to me, once, just now, when I experimented by opening a JPG with PS 2015.5 after reading this message
I set PS to Open All Supported JPGs. Tried to open a JPG and it didn't go to CR, just straight into PS.
I restarted PS, and noticed my setting was still to Open Only With Settings, so I changed it back to All Supported JPGs and then it worked, so maybe I did something wrong with setting the preference or maybe there was something slightly corrupted with the preference that required setting it more than once or setting it and restarting PS before it would stick.
In any case I'd suggest you try setting the Always setting, again, restart PS and see if it works.
If not, then go to Bridge and use right-click Open with Camera Raw and then Open Image from CR into PS, then restart PS, and check that the preference is Open All Supported JPGs Then try opening a JPG from PS, again.