Not familiar with Opera GX, but did you update your browser recently? Do you recall what/where is the last action/encounter you performed?
You can restore from this cloud code (G3WN96NF). It's not much, but a save from almost maxed chapter 1.
My last action was a mortal wound (I died) i believe, i then closed the window like i normally do, when i came back next morning it was gone. thanks for the save ill make sure to keep a cloud save available next time, opera gx might have updated (as it does often, automatically) personally I think closing the window may have been what did it but that's just a hunch.