rosserial doesnot publish imu data when combined with some other data publisher/subscriber

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I am trying to publish imu_data, wheel_velocities as well as to subscribe to cmd_vel, and some other topics using rosserial_arduino. I am using Arduino Mega 2560 and UM7 is my IMU. When i use only imu and publish its data, it publishes correctly but when I combine it with some other publishers, it does not publish imu_data at all but other data are getting published.

Below is a test program(not my original program) in which i am trying to publish imu_data and random_number.

#include<ros.h> // need this preprocessor directory for ros
#include <UM7.h>  // um7 arduino binary parser
#include <sensor_msgs/Imu.h> // need this for generating imu messages in ros
#include <std_msgs/Float32.h>

ros::NodeHandle nh;

UM7 imu;
sensor_msgs::Imu imu_msg;
ros::Publisher imu_data("/imu_data", &imu_msg);

std_msgs::Float32 random_number;
ros::Publisher pub_rand("random_number", &random_number);

void setup() {
   nh.getHardware()->setBaud(57600); // setting the baud rate for rosserial
   nh.initNode();

  // put your setup code here, to run once:
  Serial.begin(57600);
  Serial2.begin(57600);
  nh.advertise(imu_data);

  randomSeed(analogRead(0));

  nh.advertise(pub_rand); 
}

void PublishImuData()
{

     if (Serial2.available() > 0) {
        if (imu.encode(Serial2.read())) {  // Reads byte from buffer.  Valid packet returns true.
            imu_msg.header.frame_id= "/imu";
            //orientation
        imu_msg.orientation.w = imu.quat_A/29789.09091;
        imu_msg.orientation.x = imu.quat_B/29789.09091;
        imu_msg.orientation.y = imu.quat_C/29789.09091;
        imu_msg.orientation.z = imu.quat_D/29789.09091;

        // angular velocity
        imu_msg.angular_velocity.x = imu.vel_x;
        imu_msg.angular_velocity.y = imu.vel_y;
        imu_msg.angular_velocity.z = imu.vel_z;

        // linear acceleration
        imu_msg.linear_acceleration.x = imu.acc_x;
        imu_msg.linear_acceleration.y = imu.acc_y;
        imu_msg.linear_acceleration.z = imu.acc_z;

        imu_data.publish(&imu_msg); // publishing the imu data        
    }
  }
}

void loop() {  


  // put your main code here, to run repeatedly:
 PublishImuData();
 nh.spinOnce();


 random_number.data= random(10,300);
 pub_rand.publish(&random_number);
 nh.spinOnce();


}

Below is the output when i run the above program:

rosrun rosserial_arduino serial_node.py _port:=/dev/ttyACM0
[INFO] [1557145262.008324]: ROS Serial Python Node
[INFO] [1557145262.014604]: Connecting to /dev/ttyACM0 at 57600 baud
[INFO] [1557145264.122755]: Requesting topics...
[INFO] [1557145264.171944]: Note: publish buffer size is 1024 bytes
[INFO] [1557145264.172282]: Setup publisher on /imu_data [sensor_msgs/Imu]
[INFO] [1557145264.176375]: Setup publisher on random_number [std_msgs/Float32]

rostopic list shows me this:

rostopic list
/diagnostics
/imu_data
/random_number
/rosout
/rosout_agg

output of rostopic hz /imu_data

    rostopic hz /imu_data 
    subscribed to [/imu_data]
    no new messages
    no new messages
    ^Cno new messages

output of rostopic hz /random_number

rostopic hz /random_number 
subscribed to [/random_number]
average rate: 490.636
    min: 0.001s max: 0.004s std dev: 0.00048s window: 466
^Caverage rate: 490.154
    min: 0.001s max: 0.004s std dev: 0.00049s window: 939