Missing data from UART port

[Masi2018]

Hi Loboris,
I noticed that when another task is running and reads from flash memory I'll miss some of the data from uart port and don't receive the total packet. I've done some changes in the uart example code attached the source code here. I am waiting for 100 bytes starting and ending with CR character. once I receive that I'll send packet number and OK string. On the other side when OK string is received 100bytes will be sent out. I am using Docklight serial monitor rools so send the data.
Also I've created another task that reads from flash memory every one second and I noticed that when it starts reading I'll miss some of the data on serial port.
uart_example.zip

Here is the firmware output:

Here is the transmitter output: