I experienced the exact same issue this afternoon. I wasn’t even using accelerated time and after 25 minutes on autopilot the PFD froze at 23,937 feet in a step climb as well as going off course. I could not even turn off the autopilot and fly manually. I deleted the WASM folder before updating to 1.1.8. The autopilot functioned flawlessly under 1.1.6.