Bluetooth BLE - problems when transmitting and receiving long strings

Good morning,
with Mit App Inventor I created an App that every second send this string of 260 lowercase ASCII characters in packets of 20 bytes over Bluetooth BLE to a custom STM32 board with an HM-11


The same App and receives this string of 260 uppercase ASCII characters every second from the STM32 board, always in 20-byte packets


The two transmissions are NOT synchronous, APP and STM32 transmit with their own time base. Both programs check the received string and save any errors. What I notice that every 1-2 minutes a packet of 20 lowercase characters sent by the APP I find it in the message received:


I add that:

  • the messages received by the STM32 card are all correct
  • if the APP does not transmit anything, all the received packets are correct

Thanks and sorry for my english

Packets are transmitted every 0.5S and NOT every 1S. With transmission times of 1 second the problem does not occur. Sorry for the mistake

Please explain in more detail as to what your problem is?
Please show your relevant blocks and arduino/board sketches to help others help you....