Fenix 5 Elevation Gain Completely Inaccurate

I've had my Fenix 5 for a year now and on any run the elevation gain and loss is completely inaccurate. I compare my stats to my running partner and her Fenix 6 will register 5k ft gain and my watch will register 12k ft gain. We map out our runs and look at other tools to plan our long runs and my watch is always significantly off. I've done a hard reset a few times and nothing seems to work. Do I have a lemon?