The algorithm used to calculate ticks is changing. The 'upcoming' version uses a more uniform
(less heuristic) process that will hopefully work out better in most cases, so I am curious if it works for you. To try it, just change 'current' to 'upcoming' in your load call.
In general, it tries to find the largest set of ticks that are spaced (on the screen) larger than the minimum spacing, and that follow the other constraints of being multiples of a set of possible alternatives. The data range is first expanded by some percentage set by the maxPadding option, unless you have specified a viewWindow min or max, or used the viewWindowMode 'maximized' option.