I think you may be seeing the same issue my husband discovered on his iPad. If so, this is a known issue that they are working on a fix for, but there is a temporary fix you can use in the meantime. If you start Tablo, then start a show and closed caption is displaying text on the screen, press the CC button exactly one time (doesn’t matter if it is in the on or off state - only matters that you press it only once), then exit completely out of Tablo. Then restart the Tablo app. When you start your program, the CC should no longer display.
Here is the thread where I found the temporary fix to his problem. Hopefully, it will work for you as well.