This is an old bug, but in my area I have a couple tunnels that I run through, they all have a incline. My fenix 5x plus stops recording elevation changes inside the tunnel, it seems that GPS reseption has something do with it. This was also present on my fenix 5x.
I am currently running fw. 7.60 on my fenix 5x plus, but as stated above this bug is an old one.
Have attached a photo to show the problem.
