This is the one really weird one: Climbathon Profile which was before the update. Must've been the french fries after lap 4.   (Official data for the hill: Elevation Lower Tram Terminal: 306 feet (93 meters), Upper Tram Terminal: 2,334 feet (711 meters), Vertical Rise: 2,025 feet (617 meters), which is pretty close to my numbers. At the bottom of the tram, we exit below it, and they claim 250ft for the base.).

In that race, we run/hike/crawl up the hill (2000ft in 2.4 mi), take tram down, repeat for as many times as you can in 10 hrs. For some reason, it freaked out on the tram down. The profile shape and size after that seems ok, it just didn't go all the way to the bottom between laps.

I've found I get best results if I let the altitude stabilize before I start - lock onto satellites, then check the altitude window until it's constant and approximately right. I've seen it do some shenanigans then, and I've restarted the gps sometimes until it locks on. Of course, that means knowing the approximate altitude of where I'm starting. Not too big a deal. Sometimes it goes up and down while it's trying to make up its mind.

Yes, some days, it may not register the exact elevation at the finish as at the start, but usually it's within 50ft, which is good enough for my purposes.

A few times when the amount of climb seemed high, I've tried the correction here on RA or on Garmin Connect, and they've come up with higher numbers - even more unrealistic. So I keep with my conservative numbers. I've run my rolling hills enough that I know about what they should be. I've never been surprised in any races by feeling inadequately prepared - unless of course, I knew I was undertrained.