Digispark ATtiny 85 erases flash after power loss

I have some issues with my Digispark ATtiny85 board. If I upload the blink sketch for example the LED starts blinking and everything looks fine. But as soon as I unplug the Digispark from the USB port and plug it back in nothing happens. I know that the programm starts with a delay of 5 seconds so programming via USB becomes possible, but still nothing. Its seems like the flash-memory (where the programm is stored) of the ATtiny 85 is empty.

Here is the example blink sketch:

// the setup routine runs once when you press reset: void setup() { // initialize the digital pin as an output. pinMode(0, OUTPUT); //LED on Model B pinMode(1, OUTPUT); //LED on Model A } // the loop routine runs over and over again forever: void loop() { digitalWrite(0, HIGH); // turn the LED on (HIGH is the voltage level) digitalWrite(1, HIGH); delay(1000); // wait for a second digitalWrite(0, LOW); // turn the LED off by making the voltage LOW digitalWrite(1, LOW); delay(1000); // wait for a second } 

I also tried uploading the sketch from a Laptop running on Windows but without success.

I am using Linux Mint and Arduino IDE 1.8.10.

Since I am new to Microcontrollers, I would be grateful for explainations, tipps or useful links. Thank you!