The Mavic Pro disconnects can be caused by various sources from the quadcopter, remote controller, smartphone or tablet. So it could take a few of the below steps to fix the Mavic disconnect issues.

Have You Logged Into DJI Go 4 App

One of the first and easiest items to check if whether you are logged into your DJI account in the Go 4 app.  If you are not logged in, then you will more than likely have a disconnected warning at the top of the Go 4 app from the very beginning.  Login and the quadcopter and Go 4 app connect.  If you are going to fly to an area where there is no internet connection, then you should make sure you are logged before heading off.

Cables Causing Mavic Pro Disconnected Issue

Check the micro USB cable going from your smartphone or tablet to the RC. The cable could have come loose at either end. Also try a replacement micro USB cable as they can break or become frayed over time. They can even be faulty from the factory.

Damaged Ports Causing Mavic Pro Disconnects

When plugging in and out cables over time, it is possible for the port to become damaged over time.  It could be either the smartphone port or on the remote controller.  So if you are having disconnects using a smartphone like a Samsung, then flying using a tablet which uses a different port and cable.  Or vice versa.

Thanks for sharing

I found that I have to use a different cable when using an I Pad. I currently use a 10g 100w 3 foot calbe bought on amazon. I fly 30 times a month and have no issues since replaced. DJI needs to recognise this and maek a faster cable, The current cable they have is only good for 480MGPS. It is not enough to supply the new ipads