It appears that the Garmin Watch app rounds values down incorrectly.
See screenshots below:
Have just checked mine and it’s pretty accurate. There is a short delay from vrm to Garmin.
Very poor weather in southern UK today. 12kw panel!
I do have a much older Garmin Fenix 5 Plus. The rounding issue is easily repeatable for me.
Versions here:
software 19.37 (3c11a1f)
Ciq 3.3.3