All MU1 customers should run the new MU1 firmware update v1.3.4. It solves a problem that was introduced with the Roon v1.8 build 880 update of December 15th.
Due to internal changes in the communication of Roon the Grimm Audio ‘extension’ stopped working. As a result the display information of the MU1 did not show track and artist information anymore and the audio was muted until the large button was pressed. These problems are all solved with the v1.3.4 firmware update.