Does anyone here use a cable to connect the controller to there smartphone? Personnaly I had issue to connect to the controller's wifi, it always disconnect and I can't even see what I am filming...

Answer is yes, just read this forum, ther are so many post`s about using OTG cable and the pro and cons`s

Magog, in your situation, I would recommend you change a place to fly and ensure that there is no interference around your spark, such as, high voltage line, factories, metal. Please avoid bluetooth devices around your spark. Please keep us updated, thanks.