Code 400, message Bad request version ('18.0} from Network Load Balancer

My problem is that I am in the process of moving from the IoT-Core/Lambda services to a ECS docker doing containing a Mosquitto broker. This is because AWS IoT-Core does not support basic authentication and we really need this to be supported - our IoT devices have very limited resources, so we struggle very much to perform the encryption you require on the IoT-Core service. Now I have setup the docker and implemented the network load balancer, but sometimes (only sometimes) the load balancer fails to handle a simple JSON message. The MQTT message I am sending is always the same, but sometimes the load balancer fails with "code 400, message Bad request version" and other times everything is fine. When I am sending the messages directly to the Containers public IP things are always working. Also when I have the exact same docker running on my localhost and there things are also working fine. So, I think this is a problem caused by the load balancer and I am out of ideas on how solve this?

Log from where the load balancer rejets the message: 2022-10-28 06:50:3410.0.0.196 - - [28/Oct/2022 04:50:34] code 400, message Bad request version ('18.0}')8a1c1c7e0e5d4353ac68e974ce4adb99 10.0.0.196 - - [28/Oct/2022 04:50:34] code 400, message Bad request version ('18.0}') 2022-10-28 06:50:3410.0.0.196 - - [28/Oct/2022 04:50:34] "2MQTTÂ< publisherdmrfOOgG5%@2hSV8DOF1nPa80Ó
canister/outgoing{"clientid": "786523DB50583837372E3120FF181243", "elapsedHours": 1, "powerUpCounter": 1, "pressure": 1024, "valveState": 1, "stepPressureTarget": 1000, "rtcTemp": 21.0, "batteryVoltage": 18.0}" 400 -8a1c1c7e0e5d4353ac68e974ce4adb99 10.0.0.196 - - [28/Oct/2022 04:50:34] "2MQTTÂ< publisherdmrfOOgG5%@2hSV8DOF1nPa80Ó
canister/outgoing{"clientid": "786523DB50583837372E3120FF181243", "elapsedHours": 1, "powerUpCounter": 1, "pressure": 1024, "valveState": 1, "stepPressureTarget": 1000, "rtcTemp": 21.0, "batteryVoltage": 18.0}" 400 -