Near the end of the beta period, the C172's autopilot behavior was changed. It's now supposed to be more like the real world AP, but it means it has to be set up a bit differently than it was for many years.
It's been updated to :
HDG with GPSS: This setting is new as of X-Plane 11. The autopilot takes the course to intercept in VOR nav/LOC app mode from the heading bug when tracking a VOR radial or localizer. It is important that the pilot always sets the heading bug to the desired front course, otherwise the autopilot cannot intercept and track a radial or localizer. Tracking and coupling works when the correct front course is selected using the heading bug. Dual-mode intercepts to VOR radials and localizers are not possible with that type of autopilot. However, when the navigation source is the GPS, the autopilot gets GPS steering (GPSS) information and thus works with turn anticipation and can also fly DME arcs or fixed-radius RNAV legs. The S-Tec Fivty-Five autopilot works like this when installed in an airplane which does not have an HSI.