I dont know if this is happening to other people but for me it seems my chars atletics is stuck at 1 (old soldier start). I have been running around quite a lot and i have no idea wheter it is a change in Xp rate for the skill or if it is bug.
I confirm also having this issue. Athletics skill doesn't seem to increase over time. I also have no clue if it's a growth rate problem or a bug but for having my squad run for almost two days with no increase, i would trend for the bug.