nRF51 wrong sequence in received packets

[Rami AM]

I'm using nRF51822_xxAA , with SDK12.3.0 and Softdevice S130 v2.0.1 on Keil V5.29.0.0. And as a central I use Redmi 7A phone with Android V10.
I want to sample ADC @ 200Hz, and send the sample as 2 bytes inside a packet of 20 bytes (10 ADC values) at real-time. To make sure all the packets have been successfully received, I've simulated the process to generate a sawtooth signal every time ADC interrupt has been triggered, then when a 20Bytes packet is full it'll be sent over BLE, then received on the phone then saved to a file.

The problem is when I drew the data I've saved, I found there was a wrong sequence in receiving packets, for example, when I send 3 packets of data, I send them as follow:
[Packet_1][Packet_2][Packet_3]...
but when when I receive them, sometimes, I receive them as follow:
[Packet_1][Packet_3][Packet_2]...
since :
1- I've added TX_COMPLETE_EVT to the characteristic I use, and check it before sending a new packet, and that didn't help.
2- I'm creating the data packet inside adc_event_handler() and when the packet is full I set a flag, then the packet will be sent inside the main function, for (;;) loop (not app_scheduler).
3- MIN_CONN_INTERVAL = MSEC_TO_UNITS(8, UNIT_1_25_MS) = 10ms.
4- MAX_CONN_INTERVAL = MSEC_TO_UNITS(10, UNIT_1_25_MS) = 12.5ms.
5- Other connection parameters are as default.
6- my for (;;) loop, doesn't have any delay function.
7- I'm using 3 ADC channels together, all of them is being sampled with the same frequency, but I'm sending only one channel's value.
8- The phone app I use I've written it on android studio 4.1

The question is where does the problem exist? in the peripheral or central side? and how to fix it?

Thanks in advance!

[Susheel Nuguru]

Rami AM said:

Is it possible that the problem exists in the central side?, because by using nRFconnect for pc the problem didn't appear. 

It is possible, please take a look at how it is unpacking data, like the code you showed me here. 

I am quite confident that the BLE side does not have a problem since i have not heard of this issue within BLE before 

[Rami AM]

Susheel Nuguru said:

I think what you are seeing is a conflict or race condition in your code, which is a general programming issue that you need to debug. I am quite confident that this is not related to the Nordic solution

yes Susheel Nuguru it's exactly as yo said, it's a race condition between the ADC module, and BLE module, especially when I send the packet inside the main function's forever loop, after putting send function inside the ADC event handler, the problem almost didn't appear as much as before.