This happened twice.
I flew on LNAV until vectors. After I turned the plane away from the airport, using heading switch, per vectors, the A/P disengaged. When I went to turn it back on, it would not reengage from either seat.
Both times, the speed was approximately 170, the level was about 3,000 ft. FD was both on, autothrottle was on, ILS was programmed, and the plane was facing away from the airport by about 5-10 NM. The turn made from vectors instructions.
Any advice on where to look? Been flying only RJ for a short time and have most experience on Boeing. So, not sure what might be going on or some "Boeing" habit I might have kept.
Greg