I noticed this happening today on my testing GGv2 device. From the greengrass.log file I see the following errors popping up about every two minutes. Here they are grep'd out so the timing can be seen:
./greengrass_2023_12_21_19_0.log:2023-12-21T20:48:25.466Z [WARN] (Thread-4) com.aws.greengrass.mqttclient.AwsIotMqtt5Client: Connection interrupted. {reason=null, clientId=lwc-test-slynch-4, reasonCode=SESSION_TAKEN_OVER, error=Mqtt5 client connection interrupted by server DISCONNECT.}
./greengrass_2023_12_21_19_0.log:2023-12-21T20:50:26.353Z [WARN] (Thread-4) com.aws.greengrass.mqttclient.AwsIotMqtt5Client: Connection interrupted. {reason=null, clientId=lwc-test-slynch-4, reasonCode=SESSION_TAKEN_OVER, error=Mqtt5 client connection interrupted by server DISCONNECT.}
./greengrass_2023_12_21_19_0.log:2023-12-21T20:52:27.607Z [WARN] (Thread-4) com.aws.greengrass.mqttclient.AwsIotMqtt5Client: Connection interrupted. {reason=null, clientId=lwc-test-slynch-4, reasonCode=SESSION_TAKEN_OVER, error=Mqtt5 client connection interrupted by server DISCONNECT.}
./greengrass_2023_12_21_19_0.log:2023-12-21T20:54:28.515Z [WARN] (Thread-4) com.aws.greengrass.mqttclient.AwsIotMqtt5Client: Connection interrupted. {reason=null, clientId=lwc-test-slynch-4, reasonCode=SESSION_TAKEN_OVER, error=Mqtt5 client connection interrupted by server DISCONNECT.}
./greengrass_2023_12_21_19_0.log:2023-12-21T20:56:29.535Z [WARN] (Thread-4) com.aws.greengrass.mqttclient.AwsIotMqtt5Client: Connection interrupted. {reason=null, clientId=lwc-test-slynch-4, reasonCode=SESSION_TAKEN_OVER, error=Mqtt5 client connection interrupted by server DISCONNECT.}
./greengrass_2023_12_21_19_0.log:2023-12-21T20:58:30.561Z [WARN] (Thread-4) com.aws.greengrass.mqttclient.AwsIotMqtt5Client: Connection interrupted. {reason=null, clientId=lwc-test-slynch-4, reasonCode=SESSION_TAKEN_OVER, error=Mqtt5 client connection interrupted by server DISCONNECT.}
./greengrass_2023_12_21_20_0.log:2023-12-21T21:00:30.822Z [WARN] (Thread-4) com.aws.greengrass.mqttclient.AwsIotMqtt5Client: Connection interrupted. {reason=null, clientId=lwc-test-slynch-4, reasonCode=SESSION_TAKEN_OVER, error=Mqtt5 client connection interrupted by server DISCONNECT.}
./greengrass_2023_12_21_20_0.log:2023-12-21T21:02:32.069Z [WARN] (Thread-4) com.aws.greengrass.mqttclient.AwsIotMqtt5Client: Connection interrupted. {reason=null, clientId=lwc-test-slynch-4, reasonCode=SESSION_TAKEN_OVER, error=Mqtt5 client connection interrupted by server DISCONNECT.}
I'm not finding much information regarding the "SESSION_TAKEN_OVER" code.