"Jinshanling– West section of Simatai" not possible???

Last Oct 2018, I tried hiking from Jinshaling to the said west end of Simatai. However, after 2km, I was stopped by a sentry. They won't let me to the 2nd detour nor get out of the tower after it (which wasn't safely possible). That's around 3km from the starting point in Jinshaling.

Any reason for this? When will it open? Other longer trips that's possible along the Great Wall?