How to fix VO2 Max and heart rate inaccuracies on Apple Watch?

Greetings! I have an Ultra2 watch and I don't understand why my VO2 max is dropping. I just walked the same distance as I did two days ago, but faster and with a lower heart rate and my VO2 max dropped! Perhaps I don't understand how VO2 max works? My watch struggles to provide an accurate heart rate as well. I will check it as I leave the house, and it's in the 60s. I start the workout and it first logs in over 100! Usually within two minutes, it starts to drop to my actual heart rate, but then I get the spinning wheel as it tries to reset. This can last for several minutes. Once in a while, It manages to maintain my heart rate for the entire workout, but not usually. I do have a really small wrist, so I tighten the band as much as I can, but it doesn't resolve the issue. Thus, if my heart rate isn't accurate, how can any of my VO2 readings be? Any thoughts?

[Re-Titled by Moderator]

Original Title: VO2 max inaccurate/Heart rate issues