I don't have a mag but have had this using stb emu. Have you the ability to change media player on mag?
Have you changed media players
Latest firmware for MAG have issues with the CODECS. Use a older image you should be fine.
Which stb are you using and you should change your mag to 254 and media player on ljk or auto.
When I use my Chromecast on the other HDMI port then switch back to the mag HDMI port it happens to me.
A quick fix was to turn the tv off and on instead of the mag box.
I'm guessing some kind HDCP DRM stuff or something, not sure.
Did you find a solution to this, i also seem to have this problem on my mag 256. Usually happens when i am browsing through channels and change channels many times.
It happens to me but not excatly and something similar. But in my case it happens bcz the iptv is running with smart stb app which in internally operated.
But this is just a presumption