Unable to upload or remove apps from Bangle JS 2. Invalid JSON

so I cannot take a look at the console.

Well, luckily - if you're using the 'Bangle.js Gadgetbridge' you can go to 'Debug -> Get Device Logs' and then post those up. They should show all the communications between the Bangle and Gadgetbridge, which is probably better :)

I also tried this in GadgetBridge via Android Studio using LogCat

Brilliant - thanks! The issue could be other data that gets sent around that time, or it is possible that in Gadgetbridge it's to do with the way I use LocalBroadcast to send the UART data. I think somehow sometimes the packets can get mixed up/duplicated/lost on their way to the app loader.