A following MAS flight (KUL-SVG) appeared to go off track crossing the coast of MY up to about the point that flightradar lost its signal and then turned back onto track past that point.
Maybe it was WX.
Looking at the Aviation Weather Centre satellite image from 0315 UTC there was no weather of any significance between KUL and the eastern coast of Vietnam.
http://aviationweather.gov/data/obs/..._ICAO-E_bw.jpg