After encountering fog on all the Giant Battle full map clears I've run over the last 10 months, it occurred to me that based on where I had encountered the fog bug on the map that a run up the left hand side might work as a fog free quick run alternative. I recalled that some years ago I had seen a left-hand guide but if memory serves had discounted it as it required more kills. With the fog bug the cost of extra kills outweighs the lost time from 20 minute log outs.
Using this route I just completed Giant Battle in 34 minutes for the achievement with no fog. I'm not publishing that guide as it requires snow shoes to be equipped and quite a few buff kills to speed things up.
This guide however is compatible with the wiki 3 buff skilled guides and can be used as a alternative to those until the fog bug is fixed.