Same issue here.
Been through a number of suggestions from MLB fan support (factory reset, system upgrade, reinstalling the app, even tried different DNS), but this error persists.
Highlights are fine, as is live playback on every other device (Fire Stick, laptop, phone).
Like everyone else, highlights are fine, but I can't see live play or replays.
OK, so I've just spent a chunk of time on to NOW TV, and done some resets and checks, and they have told me to contact MLB on 001-512-434-1542. They actually said that they'd helped other people by having them reset the boxes, and it worked. Not sure I believe that.
So I’ve just spent a long while on the horn with MLB customer service. The 512 and 212 area code numbers don’t work- I had to use the 866 number to get the call to connect. After jumping through the hoops of the customer service agent- which of course I‘d already done- she tried to connect me to tech support but no luck. (Surprise, surprise!)
Am now waiting for a reply via email as they acknowledged the call must be costing me a fortune!