incorrect VO2 max values

You can see your average vo2max at the end of an activity to 2 decimal places in a couple of ways:

- use the free site https://www.runalyze.com (which syncs with your Connect account), and change the activity columns to display the VO2 Max (by file) metric, or in the activity details, look under FIT File details

- export an activity FIT file [open activity in connect website, select gear icon > Export File] and open FIT file with www.fitfileviewer.com. Here, VO2 Max is located in User Metrics

If you do that for the latest running activity, what VO2 Max is recorded: is it closer to 51.9x [close to what the graph indicates for 1 week ago] or is it closer to 54 [the rounded current value]?

What I have noticed is that at some point, Garmin started rounding fractional values in a funny way. Like it rounds 53.4 to 54 now, when it used to use more normal rounding rules (round to nearest integer, and round x.5 up).

Doesn't really explain what you're seeing though. It is also interesting that the graph ends 1 week ago. Have you been running since then? (The horizontal trend arrow does seem to indicate that Garmin doesn't think your VO2 Max changed recently, which could be consistent with Garmin not having any data about runs for about 1 week)

This is VO2max for cycling. Yes, I haven't been on the treadmill for at least a week. The number 54 shows me at least 2 years, even though I've never actually reached that number.

One more thing to check. VO2Max is related to your weight. Have you by accident or purpose lost few kgs recently (at least in the Garmin ecosystem)?

I last recorded my weight about 1 month ago.