u/Pristine_Wasabi1042

This is really just a bit of curiosity more than anything else, but I wondered if anyone could explain this! I'm flying LHR to YVR on Monday and have put in a bid to upgrade from PE to J, I don't have high hopes however as ExpertFlyer has been showing consistently at J0 for quite a while. Today however I noticed it's suddenly J2, but when I look at the seat map, only 1 seat is showing as available (1D). I know the seat map will often show more empty seats than are actually available due to seats not being assigned yet, but I haven't heard of it showing fewer seats than are actually available! Is this just a glitch or is there some other explanation?