since i'm doing all my outdoor walks now in airplane mode on the watch, the gps tracks, elevation, speed, pace data is perfect. As a side-effect of that, the compass app on the watch shows always exact elevation, +/- 5 or 10m, even days afterwards. Heck, even VO2 data started to appear for all my walks 🙂
procedure: go outside (with phone or not doesn't matter), watch settings-airplane mode-make sure it disables BT as well besides Wifi, back to homescreen, slide up, select airplane mode, watch workout app-outdoor walk, 3-2-1-go, wait 4-5 seconds, start walking. At end of walk wait 2-3 seconds, press end workout, press crown go to homescreen, disable airplane mode, go back to workout app-click DONE.