InkyFrame 5 cpp sleep does not seem to work properly

[r2p2]

I try to run the following code

#include "inky_frame.hpp"

using namespace pimoroni;

InkyFrame inky_frame;

int main() {
  inky_frame.init();
  stdio_init_all();
  sleep_ms(500);

  inky_frame.led(InkyFrame::LED_ACTIVITY, 255);

  while (true) {
    inky_frame.set_pen(1);
    inky_frame.clear();
    inky_frame.update();
    inky_frame.led(InkyFrame::LED_ACTIVITY, 0);
    inky_frame.led(InkyFrame::LED_A, 255);
    inky_frame.sleep(1);
    inky_frame.led(InkyFrame::LED_B, 255);
  }
}

I observe the folowing behavior:
On usb power in order:

• busy led on
• screen goes flashy flashy until it stays white
• busy led goes off
• led A goes on
• nothing happens anymore
• expected behavior would be that LED B goes on and the loop should start again

When on battery:

• busy led on
• screen goes flashy flashy until it stays white
• busy led goes of
• led A goes on
• led A goes off (since it enters deep sleep I guess)
• 60 s later ... it wakes up as expected
• busy led on
• screen goes flashy flashy until it stays white
• led A goes on
• busy led goes of
• nothing happens anymore
• expected behavior, all leds go off and wakeup after 60 s like you did it already

I would therefore assume, that sleep does not work at all when usb powered, and the deep sleep when battery powered only works once and then shows the same behavior like when being usb powered.

Don't know what I do wrong.