I also have the error mainly in GadgetBridge and Chrome in Android.
I tried this with Chrome and tried to debug via the computer (https://www.addictivetips.com/android/get-web-console-log-chrome-for-android/). But have not found a clear indication for the error.
I also tried this in GadgetBridge via Android Studio using LogCat. I couldn't see any obvious errors there either. The json string seems to arrive. I see at least log output of type UART RX with a json containing all my apps.
When I have more time, I'll take another closer look. Probably not until the weekend :(