Sad ... found several additional issues ... I used the sd card reader on an cheap 2.8" TFT Board (china) ... This has an 3.3v regulator on board caused a lot of stability issues ... so I bridged the regulator ... then it has 3x1k resistors in series in the spi lines.... in several other schematics I only find them in pull up configuration or non at all. So I bridged them ... still the mbed example works and the ported version to platfom io not.
I ordered myself a STM32f746 discovery board because it fits better for my project (TFT, Touch, Ethernet, SD card + internal flash chip - huge sd-ram ... for 50€ not a bad deal. See how far I get with this one. Hope to avoid hardware issues with this "all in one" soluition