Bug - Blueprint nodes not deletable in 4.7 preview 6

Initially there was a problem when loading my project, which was working fine in 4.7 P5. I got these errors:

Second strange thing is that shadows was vanishing when moving camera around, but only partially! :

Then problem with deleting nodes, as this topic is all about.

Final problem (and I don’t know if this is end of it) is warning message:

One or more blueprints has an unresolved compiler error, are you sure you want to Play in Editor?
level_004

I recompiled all blueprints without any problems, but message always pop up.

All start up errors appear to be fake ones, because everything is working, even after playing after warning message.

At this point I am switching to 4.6.1, because 4.7 P6 is just not working for me.

Regards,
Mox.