I suppose most of the problems you've described comes from:

1) heavy pictures. So I'm blaming the themes here
- when I use default theme of QtLockscreen then it is fast and I cannot see QtLockscreen when i slide to unlock.
2) a known bug that is described on page 1. When power button is pressed everything freeze for some time.
- this could explain rotation problems and others, like out of date info for different widgets.

I can confirm that I can see them in latest release as well.