Please try the following troubleshooting tips:
Power off you Roku, modem, and router for at least 60 seconds
Make sure you're running the most up-to-date version of the Acorn TV channel
Visit Home/Settings/System/System Update/Check now to update your system
Connect your device directly to the router via Ethernet cable.
Disconnect other devices from your network.
If the problem persists, try removing and then reinstalling the Acorn TV channel:
Press the (*) button on the Roku remote
Select "Remove channel"
Visit the Channel Store and search for "Acorn TV"
Select "Add channel"