This is caused by an issue within Settings -> L2L3 Result Options -> Stream Result Settings, there is an option ‘Source expects to receive multicast traffic from itself’. If it is disabled, then Tx port is not considered in multicast expected Rx ports. If enabled, then Tx port should be included in expected Rx ports. This issue will be fixed in 4.26.
Note: This issue is only seen when test is N*N multicast when device is both traffic source and receiver.