SARA R4 cannot detach from GPRS

[maxkraft7]

I want to periodically power the cellular module and then shut it down again to save energy. But when I detach it after sending data via a UDP socket, the device becomes unresponsive When it turns on for the second time (when detaching asynchronously) it returns at the AT+CPIN? command. I then get the response Not connected, retying from the function connectToNetwork(). It then indefinetly tries again to open a connection but it doesn't work.

Edit: Removed everything from the code not necessary to replicate this behaviour. Also I added a generous 1 mF of capacitors which greatly improved stability.

It now takes an unknown amount of time to disconnect from the network using gprs.detachGPRS(true); (in synchronous mode). As soon as I have sent the first bytes.

#include <MKRNB.h>
#include <RTCZero.h>


// initialize the library instance
NBClient client;
GPRS gprs;
NB nbAccess(true);
NBUDP udp;

RTCZero rtcZero;

void connectToNetwork(){

    auto connected = false;

    Serial.println(F("init..."));
    while (!connected)
    {
        if ((nbAccess.begin("", "hologram", true, true) == NB_READY) &&
            (gprs.attachGPRS() == GPRS_READY))
        {
            connected = true;
        }
        else
        {
            Serial.println(F("Not connected, retying"));
            delay(200);
        }
    }
}

void disconnectFromNetwork(){
    Serial.println(F("Disconnecting from network"));
    //////////////////////////////////////////////////////////////////////
    gprs.detachGPRS(true); // here the module stops responding indefinetly
    nbAccess.secureShutdown();
}

void setup()
{

    Serial.begin(9600);

    // set time
    connectToNetwork();
    rtcZero.setEpoch(nbAccess.getTime()); 

    disconnectFromNetwork();


    // endless event loop
    while (true)
    {
        Serial.println(F("New interation"));
     
         // do some measurements here every couple hours
        // every day connect to the network and upload them
        connectToNetwork();

        if (udp.begin(80))
        {
            Serial.println("udp socket opened");
            // make a udp request (i know this wouldn't work but for this example it is sufficient)
            udp.beginPacket("example.com", 80);
            // todo send multiple packets if one packet exceeds 300bytes
            udp.write("17 bytes of data", 17); 
            udp.endPacket();
            udp.stop();
        }
        else
        {
            // if you didn't get a connection to the server:
            Serial.println("connection failed");
        }

        disconnectFromNetwork();
        
    }
}

void loop() { }

The response of the device when debug is enabled (and detatching is async) on the second connection is:

init...
AT
OK
AT
OK
AT+CMEE=0
OK
AT+CFUN=0
OK
AT+CPIN?
+CPIN: READY

OK

and after that it just stops.