Flashing Atmega328PB only works once

I am using atmega328pb-testing (1.1.2) from watterott with a custom board.
Furthermore I've installed Arduino AVR Boards 1.6.207

the board makes use of a 100nF cap and a 10k resistor for handling reset functionality.
everything is 3.3V - the atmega328pb board as well as the FTDI programmer.