Cannot write more than eight times in the same characteristic

[j99ht]

I'm trying to write several times the same characteristic,. However after eight times, my script is still writing but the device is not receiving anything. Even more, I can disconnect and connect again, but when I try to write, the device is not receiving.

Now, if I disconnect and I use a mobile app, the mobile app is able to connect, to write and the device is receiving.

Below my code

scanner = btle.Scanner().withDelegate(ScanDelegate())
devices = scanner.scan(10.0)
string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

def chunkstring(string, length):
    return (string[0+i:length+i] for i in range(0, len(string), length))

for dev in devices:
    print "Device %s (%s), RSSI=%d dB" % (dev.addr, dev.addrType, dev.rssi)
    for (adtype, desc, value) in dev.getScanData():
        print "  %s = %s" % (desc, value)
        if desc == "Complete Local Name" and value == "Device name":
            print "FOUND Device"
            p = btle.Peripheral(dev.addr)
            svc = p.getServiceByUUID(service_uuid)
            print(svc)
            ch= svc.getCharacteristics(char_uuid)[0]
            print(ch)
            for chunk in chunkstring(string, 20):
                chunk
                print valueToWrite
                ch.write(valueToWrite,True)
                print(chunk)
            break

Any idea about what could be happening?