while reading a binary file from zmq plugin I'm getting packets with num_samples = 21?

[DhyaniBharat]

I have a pre recorded binary file with data size (2846720, 136).
I am using this file to stream the data with ZMQ plugin.

Here is the output from ZMQ:

header === {'message_num': 129072297, 'type': 'data', 'content': {'stream': 'Rhythm_FPGA-100.0', 'channel_num': 0, 'num_samples': 21, 'sample_num': 19930281, 'sample_rate': 1000.0}, 'data_size': 84}
header === {'message_num': 129072298, 'type': 'data', 'content': {'stream': 'Rhythm_FPGA-100.0', 'channel_num': 1, 'num_samples': 21, 'sample_num': 19930281, 'sample_rate': 1000.0}, 'data_size': 84}

1. Why am I only receiving 21 samples at one time.

[I tried it with the default file from openephys tool: that gave out 853 samples at a time]
What does the num_samples that are received depend on?

2. From the data packets received it looks as we are receiving all the packets concurrently.
So for comparing the data, I took the 1st channel data from the original file and compared it with the 1st channel data received from the ZMQ stream.
The data read from original file is in int16 format
while data from stream is in float32 format. So I converted the stream data to int16.
But I wasn't able to find the continuous chunk of the stream data in the original data.

So my question is the why the stream data different that the original data of the file?