The cause may be that the data flash erase processing in the program was executed. The program starts running when the microcontroller is powered on. After that, when the debugger is started with LEXIDE-U16, the debugger stops the program. If the program executed before starting the debugger includes data flash erase processing, the data flash area will be erased. As a result, it appears that the data flash area is initialized when the debugger is started.