It sounds like the Original (full res) is in the Cloud, with the Smart Preview (lower res) store locally. It probably requires the Original to export, so you will have to turn sync on to get this.
Two things you could do to help are, in Settings, Cloud Storage, turn off Only Download Smart Previews, this will keep more Originals locally. Although the best options is to select an Album and Store Locally, which will download all the Originals for that Album, although this will take up a lot more space on your device.
I work for a sports newspaper and usually shoot with jpeg and raw simultaneously and edit on the go by just importing the jpeg files directly to my iPad but I also import raw files occasionally when I need a more extensive correction on some specific photos.
At home, with more time and attention, I import the raw files to a drive which I keep for archive and I do a more extensive edit using Bridge and ACR for the newspaper own archive.
With this workflow I use the Lightroom Mobile as a standalone platform and although I understand the capability and convenience to some users I would love to have an option to completely disable the sync function as simply pausing it just has the inconvenience that when exporting the images to any destination other than the Camera Roll option it stops due to some photo stuck in a sync.