Autocompletion suddenly stops working in clang code model

I am using clang code model, and autocompletion suddenly stops working. In the same time, QtCreator still underlines by red erroneous line of code (if any) and shows me messages from clang (like: no viable conversion from ... to ...).

How can I help to investigate the issue?
(I know you have some environment variables to define to see debug output...)

QtCreator built from 3c84693907665bf333d7882340baba5c760bfb46, but it also happened when it was built from master branch prior to 3.3 branch.

*EDIT*
QtCreator still able to autocomplete local variables like
double Variable;
but can not show me member functions of some class.