I am having a similar problem.
I have a DJI P4, using an IPAD air 2 ios 11.2.6 with the DJI Go4 ap (4.2.6). I have the video cache set to re-write itself.(I also have no HDMI module)
During flights, the App will freeze. Just hang. The first time it did it, I panicked. Now it does it once...