I played around with various settings and figured out, that the sampler created in the Host Program (i.e. the C++ code), which was then passed to the GPU as a parameter (as i wrote before, this had to be done, to work on my boss' NVidia GPU) doesn't work as it should in 2.3
Now, some image-access still works: This means, that i can read values from images with the sampler and, for example, write them to a outputBuffer. What seems to be a problem is accessing the image inside loops with changing parameters/coordinates. In the end i got the same results for all iterations of the loop, which was the major problem I had.
When i create the sampler inside the OCL code (just after the pragmas), it works just like it should. It looks like this: