Could be the video format it doesn’t like. Download MediaInfo, open a troublesome file, select treeview and export the results to a text file. Post the text in a post, so we can have a look to see what might be the problem. Do the same with a file that plays OK.
MP4 is a container not a digital compressed video format.
You can buy cheap portable hdmi players (about £20.00) that support many more video standards using USB.
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