@stevena Same issue with the Spartan Sport WHR. I asked about it on here a while ago and was told the following:
“There’s a threshold, which is 3 meters for baro watches and 7 meters for watches without baro, and the total ascent / descent increment in chunks once the altitude change exceeds that threshold.” (copy-pasted from here: https://forum.suunto.com/topic/3886/dodgy-elevation-on-spartan-sport-whr/5)
In other words, if you’re running a route that undulates by less than 7 metres at a time, your non-baro watch will treat it as flat.
I find this super-annoying too. But apparently it’s considered OK in Suuntoland, because I was told I was being nitpicky for considering it bizarre. If it’s any comfort, I have a Stryd and it isn’t much better for elevation. Under-reports by almost a factor of ten on some routes, so perhaps there’s a similar arbitrary threshold at work there.
Update, 26 April: Just for the record, I may have been mistaken about Stryd’s accuracy, or perhaps I was looking at the wrong .fit files? At any rate, lately I’m getting conspicuously plausible elevation data from Stryd.