Apple Watch/Fitness Altitude accuracy extremely inconsistent, at least on bike rides

I'm finding altitude accuracy extremely inconsistent. For 2 exact rides (e.g. same outdoor course) the Fitness App was showing altitudes of 3376 ft and (Over a 37.46 mile course) and 4216 ft (Over a 38.15 mile course). The 4200 is likely the more accurate one. I'll do another course and also run it with Strava for comparison, but is this normal? (Overall pretty disappointed with how accurate this watch is; similar problems when swimming, whether pool or open water). It's an Apple Watch Series 9 with 11.6.1 (22U90) watchOS