Describe the problem

To reproduce

This is very difficult to reproduce and, after a lot of trial and error, we found a combination of HW and SW that is more likely to reproduce it:

• A macOS machine
• A board that mounts a CP2102 chip as a USB-2-serial converter

Here are the instructions to reproduce:

1. Upload the following sketch to the board (note it is configured for 9600 baud):

   void setup() {
     Serial.begin(9600);
   }
   void loop() {
     Serial.println("Hello, world!");
     delay(1000);
   }

2. Open the Cloud Editor Serial Monitor
   ✅ The serial output is printed without corruption (Cloud Editor Serial Monitor always starts configured for 9600 baud).
3. Select "115200" from the baud rate menu.
4. Select "9600" from the baud rate menu.
   ❌ The serial output is corrupted with swapped or missing characters, as described by the users.

The fault only occurs when changing the baud rate in the Serial Monitor. It is not specific to the 9600 baud rate. For example, I can also reproduce the fault with this more simplified procedure:

1. Upload the following sketch to the board (note that I configured it for 115200 baud instead of 9600 this time):

   void setup() {
     Serial.begin(115200);
   }
   void loop() {
     Serial.println("Hello, world!");
     delay(1000);
   }

2. Open the Cloud Editor Serial Monitor.
   ✅ The serial output is corrupted as expected because the Serial Monitor is configured for 9600 baud.
3. Select "115200" from the baud rate menu.
   ❌ The serial output is corrupted with swapped or missing characters, as described by the users.

Expected behavior

The Serial Monitor shows uncorrupted output.

Arduino Create Agent version

1.7.0

Operating system

macOS

Operating system version

Sequoia

Browser

Chrome

Browser version

135.0.7049.115

Additional context

Additional reports

• https://forum.arduino.cc/t/arduino-uno-with-garbled-serial/1354153

Issue checklist

• I searched for previous reports in the issue tracker
• I verified the problem still occurs when using the latest version
• My report contains all necessary details