This one looks like the same issue: https://github.com/espressif/esp-idf/issues/2687
It mentioned as closed, but actually, it doesn't
So I'm using ESP-IDF release v4.0 with all the latest updates and can face it again...

Hi there, Looks like I face a bug in Bluetooth interrupt handlers. It happens when OTA task is writing chunks of downloaded image to the flash and at the same time BLE GATT server gets some read/write requests from the client So based on my investigation, the root causes of the issue could be relate...