What are these CAN frames / messages?
What you see looks like remote frames: it's a feature of the CAN bus which allows to transmit certain frames on request rather than periodically. Simply put, a regular frame is transmitted by a single node, first ID, then length, then data. With a remote frame, the node which wants the data transmits the frame ID and length plus a special bit (RTR), and waits for the node which handles that frame to transmit the actual data.

448#**R4** means that a node has requested the remote frame with ID of 448 and DLC of 4, but nobody on the bus volunteered to supply the data.