Not to defend DJI's customer service or anything (I've never used their customer service yet and hope I never have to), but it's silly for us to expect their online chat folks to know more than what we have available to us in the manual or in these forums. Just a sad fact of the state of online customer service for any company really, especially with a brand new product like the Spark where they haven't built up a sufficient knowledge base for the customer service reps to search and get canned answers to common problems.
Anyway, as far as we know, when using ActiveTrack without an RC connected, the Selfie photo is really just a screen grab from the 1080p video, hence it's lower quality. I personally think this is a software issue because if you have the RC connected, put it in gesture mode and snap a selfie, you get full 12MP quality.
I did laugh that they told you to put the setting in JPEG+RAW. LOL Since RAW isn't an option on this device, and probably will never be (reports are that the processing power required to save in RAW creates problems elsewhere on the device, hence the engineering decision to only support JPEG).