Yup, this was fixed a month or two ago but seems to have reared its head again in the last week for me.

i've got the same issue. really frustrating

To temporarily overcome the problem, keep the space station selected when going from level 4 to 5 and play for a while, after a while you can click as you like and there will be no crash.

This was the solution I came up with to get around it while it isn't fixed.

Another work-around, even though it's not as fun, is to disable heroes. When preparing the skirmish, go into the advance options and un-click the "Allow Heroes" button in the top left. I found that prevents the crashing, because it used to crash on me every single time when I had heroes enabled.