30sec until BLE Nano v2 comes up


On my pcb (with proper 5V input) the onboard LED is flashing for around 30 seconds and then the script starts properly.
If I put the BLE Nano v2 into programming module it starts promptly.
What might cause this delay? What is a fast flashing LED meaning?

Pins 1 to 5 are used as Analogue input
D6, D7, D8, D9 are digital outputs.


After removing the connection to pin 4 and 5 (originally used as analogue INPUT) it starts up immediately and everything works fine.

Has anybody ever used pin 4 and 5 as input pins?

Note: During the 30seconds of blinking pin 4 was on 0V, but I measured around 1V on pin 5. This signal was gone after it finally booted.