I'm not so sure is it the patch 1.9 causing lag in MP recently.
Before I installed the patch 1.9, it is enough smooth when I playing in MP.
I didn't installed or used the DX11 patch, so it may relate to patch 1.9 or other problems in my PC.
So, I want to know is there anyone have the same problems?

yup same problem here.
been smooth since release day until 1.9 and now i get the odd lag here and there.

Also DX9 got some lighting upgrades. Poorly done as we know it from Crytek, so it ruins the performance you know from your PC....