Same problem here - unbelievable, but true. On our brand new LG OLED TV 55BX many DNLA video files even become unplayable from one day to the other.
So far I fixed all of the above disasters by unplugging the network cable for a short moment. That refreshes all DNLA files and also fixes the "unable to play" bla bla... Even the "refresh" option in the top right corner didn‘t help. It refreshes the list of extern storage devices.
Thanks to all these huge companies for spending millions in marketing rather than functioning. I know its not easy - being a software engineer myself - but there seem to be far to few of them amongst the management.