ESP32: Arduino 1.8.13 – issue with BluetoothSerial.h

[airfish]

Hi Everybody,
I’m reading within a loop 2 ADC channels (ADC 1-5 and ADC 1-7) and transmit the readings together with the actual millis() value via Bluetooth serial (librarie: "BluetoothSerial.h" - command: SerialBT.println(outputString);) to an Android device (app: Serial Bluetooth Terminal with buffer size: unlimited).
Everything works fine and I realize 4 to 5 datasets per msec. But after some time (15 to 50 milliseconds) the process stops for 10 to 100 milliseconds. Then the process continues as expected up to the next stop. With increasing process time there is an increasing stop time. It looks like a buffer is filled and must be cleared.
Has anybody a better explanation and more important an idea how to overcome the issue?
Many thanks for your help in advance.