Session Flashdata Persisting Like Normal Session Data

Got there in the end.

I tried to switch back to using the File Handler rather than Database Handler session driver to see if that helped. However, I then started getting an error message from CI framework about setting ini as the session was already started.

After much wasted time in transpires that another library that I was loading via composer (also recently added) was starting the session in its autoloader and messing with sessions. Removed this library and now all is well again.