B737-800 First Officer reported the Autopilot malfunctioned on an approach resulting in a temporary loss of control. Flight crew disengaged the Autopilot and continued the approach.

Narrative

During the approach; First Officer Pilot Flying (PF) was given an aggressive descent and vector to intercept the localizer for ILS XXR into ZZZ. It was night time with very gusty winds but VFR conditions. We overshot final and were given a vector back to intercept. Our energy state was appropriate. Autopilot was on and APP (Approach) was appropriately armed. We were fully configured with the Before Landing Checklist complete approximately 1.7 NM from the FAF. About 3 seconds after GS intercept (2100' MSL; ~7 NM from touchdown); the Autopilot commanded a climb. We climbed approximately 200 feet; then the Autopilot commanded an aggressive descent. Vertical Velocity Indicator reached 2000 FPM momentarily and slightly more than 2 dots below glideslope. First Officer PF appropriately turned off the Autopilot; raised the nose; maintained airspeed; and climbed to reassure the glideslope. We were never below 1000' AGL; and were stable by 1000' AFL. Looking back; we think that a better decision may have been to execute an immediate go-around with such a serious Autopilot malfunction. Alternatively; we could have turned off the Autopilot slightly sooner. However; we were VMC and felt that it was safe to continue once reassuring the glideslope. The landing was uneventful.Unknown causal factor; however; disengaging the Autopilot during gusty wind conditions or even after the initial uncommanded climb occurred may have prevented the increased vertical speed.