I have a Roku Ultra and two Roku Premiers. Media player played audio content from my USB hard drive for more than a year and suddenly does not work. I can see the content but nothing will play. No error message. I HAVE FOUND ROKU SUPPORT TO OBYSMAL AND NON EXISTENT. Great product but absolutely no support. Using COVID-19 as an excuse not to answer technical support phones. No email and no chat support. Nothing. I would never have purchased these products had I known about their horrible support. Will never purchase another Roku product.
UPDATE - Might not even be able to post this as I'm getting an error message regarding my post that reads "Correct the highlighted errors and try again". There are no errors highlighted!
When you say "media player", do you mean the Roku Media Player or some other one? If RMP, then there was a recent update to version 5 that caused a lot of problems for some. If you have that version, try to "update" to version 4 by pressing the asterisk button (*) when you have the channel highlighted on the Roku home screen.