Since this is occurring regardless of Core machine, it sounds like there may be some networking troubles at play here. Is your Core connected via Ethernet directly to the router or are there any switches / other networking hardware involved? What kind of router is in use?
Can you clarify the above? You mentioned that they play fine via System Output, but also that they’re getting the same error. Is System Output working as expected?
Can you try logging out of TIDAL in Roon and logging back in? Is there any change after?
its not my network please read thread ive already answered yes ive connected via ethernet no system output plays the file but still shows the same slow network message its the same tracks over and over other tracks play ok