The RX 1 / RX 2 DSC start / Stop message is a completely normal message and is not an indication of a fault or problem.
Essentially, it’s just a text message indicating when one of the AIS receivers has started/stopped a DSC channel management listening period. Class B equipment (like the B100 and B300) is required to listen to channel 70 (The DSC channel) periodically at specific times defined in the standards, for DSC channel management commands. As Class B lacks the third receiver necessary to do this full time it is achieved by occasionally switching an AIS receiver to this channel.