RAK11300 LoRa Module OTAA/ABP Example does not send payload with serial monitor attached

[ThomasLeister]

Hey! I just got into the RAKWireless ecosystem and I've been experimenting with your RAK11300 examples when I noticed a strange issue: It seems like the example program does not send any actual LoRa payload messages when being connected to the Arduino serial monitor at the same time.

The log says:

=====================================
Welcome to RAK11300 LoRaWan!!!
Type: OTAA
Region: EU868
=====================================
OTAA Mode, Network Joined!
Sending frame now...

and I can see the device join in ThingsNetwork:

... but no payload message (every 20 seconds) is received. Just join-related messages, then nothing.

This only seems to occur when the Arduno Serial Monitor is attached to the device. Under the following conditions the example code works fine:

• Device connected to external USB power source, no laptop attached via USB
• Device connected to laptop via USB, but no serial monitor attached or Arduino IDE running
• Device connected to laptop, Arduino IDE is running, board is detected but serial monitor is not opened/attached

Only if the serial monitor is attached, the problem occurs and the example code seems to get stuck / freeze at "Sending frame now...".

SW versions:

• Arduino IDE 2.3.3
• WizBlock LoRa example for RAK11300 @ 68173da
• SX126x-Arduino Library by @beegee-tokyo 2.0.27