SerialOTG: list index too large

I developed ble tilt sensor application and I use serial cable to write the new offset value into microcontroller using serialOTG extension. The app was being okay for a year and now It has an error as per the screenshot. how do i fix this? thank you.

How do you know where one message ends and the next begins?

Your list for 7 items, you want to take as many as 16 items from this list.