After a connection is created, there is no NDI output or very low frame rate on the RX endpoint. Please try to use NDI Time Stamps as Timecode handling.
Low frame rate could also indicate poor hardware performance.
If there is no FPS shown on the RX side of the connection (In the Connection details - Right click on the thumbnail and select "Show Details", it could be an indication of the NDI source not carrying any audio frames. In that case select the "No Audio" option when creating or editing the connection.