OK - well, almost immediately after posting this, I retried making a direct copy of my project, and it seems to work now -
The only thing I did differently was to open the project with 4.6 by accident, I forgot to switch engines, then I compiled for 4.7 and re-started and it seems to be fine now.
Here’s the steps I took (albeit inadvertently) in case anyone else runs into a similar situation:
1 - Copy the project to new location
2 - Build the project in its current engine
3 - Change the engine
4 - Rebuild and run
Well - sorry about spamming the hub!