VO2 Max Rapidly Dropping

I've had my vivoactive 4s since the beginning of the year. My VO2 max has always been between 46 to 48, but within the past week, it's plummeted to 43. I haven't done anything different to my fitness routine. It's a bit upsetting because I went from the "top 5%" to the "top 20%" which a pretty huge drop for absolutely no reason. 

I turn off my watch every night, so it isn't a turn it off, turn it on sort of fix. I update it every time it prompts me to. 

I've also noticed that it will sometimes tracks my intensity minutes and sometimes not doing the same exact exercise. 

I cannot think of any reason that my VO2 max would drop 5 points in about a week. It doesn't make any sense. Does anyone know why?