When a 3D+t image is loaded that has an arbitrary timegeometry because the time-distance between the first and second timestep is longer than the time-distances between the following timesteps, not all timesteps are correctly displayed.
Cause of this issue is, that the rendering-geometry is always a ProportionalTimeGeometry that uses the distance between the first two timesteps for all timesteps.
When rendering the scene, the BaseRenderer calculates the timepoint 'tp_render' from the rendering-geometry for the current timestep. Afterwards, the image-geometry is asked for the corresponding timestep.
However, as the rendering-geometry consideres all timesteps to be equally-distanced there is a mismatch in the timestep-to-timepoint calculation between rendering- and the image-geometry that causes a wrong image-timestep to be shown for the current rendering-timestep.
A potential fix would be to Extend the SliceNavigationController to be able to use an ArbitraryTimeGeometry instead of a ProportionalTimeGeometry.
However, I'm not quite sure what that would cause if you mix images with ArbitraryTimeGeometries and ProportionalTimeGeometries.