QwtPlotzoomer for more 4 -yleft axis

[Uwe]

In general the idea of your implementation should work, maybe beside of one aspect: all of your zoomers are connected to the same x axis. If it is not a dummy one you will have some unexpected effects.
Assuming that xBottom is your common x-axis and you don't use xTop, I would connect only the first zoomer to xBottom all others to xTop. In case you need xTop and xBottom you could add an invisible dummy x axis.

Why things are not working in your application is hard to say from the code snippets. But as you have a crash I would start with a debugger session.

Uwe