Sometimes when you burn spruce twigs on the end of the trail and wait around, it doesn't work. I have a save available of a character in this situation, Reko.
I got the quest, killed the lynx that was in the area (I've noticed that the farm animal won't come if the predator is nearby but maybe that's just a superstition?) and skinned it and cooked it's meat and then I went back to the pig tracks and followed them to the very end.
I cut spruce twigs from the tree nearby and then without picking them up lit them on fire (maybe this is the problem? maybe i should have picked them up and then dropped them again?)
i waited for about 2-3 hours, no pig.
I tried lighting fires one at a time on the empty tiles surrounding that one, just in case there was a track there that I missed, waited a couple hours for each one, didn't work of course. I haven't burnt a fire on any of the other spaces with tracks so the trail should be preserved. I've tried tracking all around that area in places where i couldn't see tracks, just in case there was a gap in the trail and it continued but i'm pretty sure i was in the right place.
My character is saved standing on the burnt ashes of the fire that was on the last track in the trail. no pig anywhere