I'd say don't discuss, just rebuild it using the recommended and standard way to control the contrast.
Just so you can rule out (or not) that this leads to your issue.
Also, if you are using a breadboard, either re-wire it using other contacts, or get rid of it for now.
Breadboards are nice for quick and easy prototyping, but always expect poor contacts.
All of us can't wait for you to return home so you can go on with your experiments.
So do tell us about what you found, when you find out what's going on.