  Circumplanetary discs can be linearly unstable to the growth of disc tilt in
the tidal potential of the star-planet system. We use three-dimensional
hydrodynamical simulations to characterize the disc conditions needed for
instability, together with its long term evolution. Tilt growth occurs for disc
aspect ratios, evaluated near the disc outer edge, of $H/r\gtrsim 0.05$, with a
weak dependence on viscosity in the wave-like regime of warp propagation. Lower
mass giant planets are more likely to have circumplanetary discs that satisfy
the conditions for instability. We show that the tilt instability can excite
the inclination to above the threshold where the circumplanetary disc becomes
unstable to Kozai--Lidov (KL) oscillations. Dissipation in the Kozai--Lidov
unstable regime caps further tilt growth, but the disc experiences large
oscillations in both inclination and eccentricity. Planetary accretion occurs
in episodic accretion events. We discuss implications of the joint tilt--KL
instability for the detectability of circumplanetary discs, for the obliquity
evolution of forming giant planets, and for the formation of satellite systems.
