Kerog,
First thing to do is check your rinse aid, make sure there is some in it and that it is decent quality stuff.
Next check that the spray arms are clear, you can take these off to clean them and that they can spin free unobstructed by plates, cutlery or fresheners.
After that you need to check the load pattern you use ensuring that it’s no just certain areas that are affected, if that’s the case then you need to look at the loading.
In 99{e5d1b7155a01ef1f3b9c9968eaba33524ee81600d00d4be2b4d93ac2e58cec2d} of cases the above points will cure what I think you’ve got there which is tiny particles of dirt being trapped and them hardened during the dry process.
Hope that helps.
K.