Rosserial deserialization error when receiving Serial2

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I'm very close to getting my robot project working the way I had hope. A summary of the structure is that I have a Raspberry Pi 2 connected to 2 Arduino MEGAs: 1 for motor control and sensor connectivity and another for interfacing with an NMEA0183 marine sensor. I have been able to receive serial data from the sensor separately but when I connect to ROS and rosserial, I get the following error:

Traceback (most recent call last): File "/opt/ros/melodic/lib/rosserial_python/serial_node.py", line 89, in <module> client.run()

File "/opt/ros/melodic/lib/python2.7/dist-packages/rosserial_python/SerialClient.py", line 540, in run self.callbackstopic_id

File "/opt/ros/melodic/lib/python2.7/dist-packages/rosserial_python/SerialClient.py", line 111, in handlePacket m.deserialize(data)

File "/home/ubuntu/ros_ws/devel/lib/python2.7/dist-packages/floatbot_msgs/msg/_Float64Stamped.py", line 110, in deserialize genpy.message.DeserializationError: unpack requires a string argument of length 4

[depth_serial_node-3] process has died [pid 4523, exit code 1, cmd /opt/ros/melodic/lib/rosserial_python/serial_node.py __name:=depth_serial_node __log:=/home/ubuntu/.ros/log/2770e2da-3a91-11ec-9518-0f4138ab90b7/depth_serial_node-3.log]. log file: /home/ubuntu/.ros/log/2770e2da-3a91-11ec-9518-0f4138ab90b7/depth_serial_node-3*.log

Here is the loop() function of my Arduino code:

void loop() {
     nh.spinOnce();

    if (isConnected && !nh.connected()) {
    relayOutput(false);
    } else if (nh.connected()) {
    t.update();

    if (Serial2.available()) {
        parser << Serial2.read();
    }
   }
   isConnected = nh.connected();
}

When I remove the parser section (that is read from Serial2), I don't get a crash but of course that means my data is no longer read. The Float64Stamped is a custom message type.