Hello again!
Thank you for your update. Considering you have covered all steps, and no clear error shows up in blueprints and code, yet the issue remains, the problem is most likely tied to an under the hood interaction between your project and 5.6.
Since this version of the engine has just released, it is still prone to unexpected behaviours. I would suggest sticking to 5.5 for the moment, until a hotfix is deployed, then you can test again.