Hello I have had the same issue with 3 different Mavic minis. I have a new iPhone XR and my phone has 0 connection issues with anything except for the Mavic mini . 
I returned the first one I had and got this second one and I am having the same connection problem. I have tried 3 other cords including a new longer cord purchased from amazon. I was going to just return the mini today and forget about trying a third one unless anyone has any suggestions?

I returned the first one I had and got this second one and I am having the same connection problem. I have tried 3 other cords including a new longer cord purchased from amazon. I was going to just return the mini today and forget about trying a third one unless anyone has any suggestions?