Hello Søren,
The crashing problem will be fixed in the next update, but the "vertical datum error" might appear if the coordinates input to the Reference pane do not correspond to the area defined in the GeoTIFF related to the geoid model.
I've just used the same combination (ESPG::5850) and specified coordinates for three points inside the area of use, according to the EPSG-registry. It worked without error message.