Debugger not displaying 'this' and all variables

I am using QtCreator

Qt Creator 4.2.1
Based on Qt 5.8.0 (GCC 5.3.1 20160406 (Red Hat 5.3.1-6), 64 bit)
Built on Jan 20 2017 01:20:15
From revision 7071b61e02

At some point the debugger watch window has stopped working properly, I know that previously I have been able to expand pointers and drill down into the class to reveal the state of members. In a lot of cases now I get the pointer displayed and then <not accessible> where the address would normally be displayed, if I attempt to expand the pointer it shows just [0] and nothing else.

Parameters do not always appear in the "Locals and Expressions" window either. I've also noticed that 'this' no longer appears when debugging an object.

This is making development very difficult. The question is, is this an option hiding somewhere or is it a bug?

Kind Regards,
Simon Platten