Any long flight I do over 10 hours the aircraft leaves the programmed route and heads off into the sunset. Somethings wrong , do not struggle with other developers aircraft. I do not have any discontinuities programmed. Latest flight from EGLL to SCEL left the route after 12 hours and turned right and headed off on its own. This is the 5th time I have tried a long route to no avail. Routes programmed from Simbrief.