Step 1:
I have installed the driver.
I have M5 Burner v3 beta.
I can find the download for UIFlow_StickC_Plus2 v1.13.2.
I have configured it as follows:
Internet mode
flow.m5stack.com
Wifi credentials
COM.X true

Step 2:
I burn the code to the device
The M5Stack Stick C Plus 2 reboots and shows the splash screen (API key and "cloud").
The device appears as online in my router connections table.
On https://flow.m5stack.com/ I press the connect button and it shows as connected.

Step 3:
I add some basic blocs - e.g. change the background colour of the screen.
I run it on the device - success
I download it to the device - success

Step 4:
I make a change to the blocks.
The device shows as disconnected, and pressing download shows "Upload code failed, maybe your device is offline check it and retry".
The device also shows as offline on my router portal.

Step 5
I return to M5Stack Burn.
I go back to configuration.
The config mode is now set to App Mode.
I change it back to Internet mode.

Step 6:
I can now connect and download

What is App Mode and why does the device keep defaulting back to it?

I should also let you know that I have the USB C cable attached throughout the above process.
If I unplug the device after burning, it appears that this issue doesn't happen. The device stays connected and I can download repeatedly.

Thanks
Brendon