  We study the stability of systems of three giant planets orbiting 3 - 8 M_Sol
stars at orbital distances of >10 au as the host star ages through the Main
Sequence (MS) and well into the White Dwarf (WD) stage. Systems are stable on
the MS if the planets are separated by more than ~9 Hill radii. Most systems
surviving the MS will remain stable until the WD phase, although planets
scattered onto small pericentres in unstable systems can be swallowed by the
expanding stellar envelope when the star ascends the giant branches. Mass loss
at the end of the asymptotic giant branch triggers delayed instability in many
systems, leading to instabilities typically occurring at WD cooling ages of a
few 100 Myr. This instability occurs both in systems that survived the star's
previous evolution unscathed, and in systems that previously underwent
scattering instabilities. The outcome of such instability around WDs is
overwhelmingly the ejection of one of the planets from the system, with several
times more ejections occurring during the WD phase than during the MS.
Furthermore, few planets are scattered close to the WD, just outside the Roche
limit, where they can be tidally circularised. Hence, we predict that planets
in WD systems rarely dynamically evolve to become "hot Jupiters". Nor does it
appear that the observed frequency of metal pollution in WD atmospheres can be
entirely explained by planetesimals being destabilised following instability in
systems of multiple giant planets, although further work incorporating low-mass
planets and planetesimals is needed.
