To avoid floating inputs, it is a common design practice to connect unused MCU I/O pins to ground. If your source code by mistake configures one of the grounded I/O pins as a logical 1 output, a high current might be drained on that pin. This high unexpected current is easily observed by reading the current value from the Power graph in the Timeline window. It is also possible to find the corresponding erratic initialization code by looking at the Power graph at application startup.

A similar situation arises if an I/O pin is designed to be an input and is driven by an external circuit, but your code incorrectly configures the input pin as output.