I received my mavic on Tuesday and it has been working great. This morning I took a short test video in 2k. Then I was able to watch the video in 2k on my Galaxy s6 by using a micro SD to micro USB connector. This evening I went to fly, however there was a new firmware, so I updated it. I recorded in 4k for the entire flight. When I went to play the video on my phone via the micro SD to micro USB connector I got a "can't play video" error. I tried recording in 2k and 1080 but got the same error. The only difference I could find was under properties of the video. The video which will play has a tag of v01.03.5490. The videos which will not play have a tag of v01.04.5523.m y guess is that some setting changed when I upgraded the firmware.

Have you checked the settings of the video, such as format.
After firmware upgrading, maybe the parameters have been changed.
Please double check it and record videos again to have a try.