I just focus on the trend rather than the value. Last year, after being infected by two viruses in parallel my vo2max plummeted from ~55 to 40 in a month. It correlated with how I felt, like 15 years older. It took me six months to get back to 55, and then it stayed around that value quite consistently, viruses or not.
Similar for me, but I've also not really seen my behavior influence it too much. I clearly have better and worse weeks / months, where I might walk at 10min/km and require a 90-95 HR to do that, and worse months where I'll only walk at 11min/km and end up in the 100-110 HR range, but it's not like my exercise levels or weight or nutrition or anything would differ much between the two, they are all very consistent. Likewise when I increase cardio training I don't see any correlated change in VO2max. That also makes sense, as VO2max is famously difficult to train.
I suspect for me and probably many others in the "acceptable fitness level" category the main factor influencing what ends up being reported as VO2max is stress, both physiological and psychological. That correlates real good. At least for me.
In my experience, vo2max doesn't seem to correlate with stress. I've been stressed out for the last few weeks at $dayjob, and my vo2max has been consistent with more relaxed periods (high). How much of a variation do you perceive during stressful periods?
