Bangle.js App Loader returns "Upload failed, Unexpected response"

Hello, I would like to upload an app using the Bangle.js App Loader. My watch was broken so I had to reinstall a new firmware. Now there is the firmware 2.08 of bangle.js installed (but no settings or clock). This implies that it boots to the Bangle.js logo but nothing more.

When I tried to upload the bootloader, it fails with the error "Upload failed, Unexpected response" display in an orange box.

Do you have any idea what might have caused this error and how I could fix it? I can connect to the bangle.js through the Web-IDE. I also tried to enter

require("Storage").eraseAll();

in the console. It returns undefined.

When I try to execute some code, I get this error:

Uncaught InternalError: Timeout on jshFlashWrite
 at line 1 col 170
... 1000);\n}, BTN2);\n",0,116);,

for this sample code:

setWatch(() => {
  E.showMessage("You\npressed\nthe middle\nbutton!");
  setTimeout(()=>g.clear(), 1000);
}, BTN2);