thank you for your answer.
I did some investigation on the problem the last few days:
You were right regarding the tool extensions, they are the problem. However, (un-)checking “Remove Tool Extensions” doesn’t change the problem. It seems that DNG doesn’t like the tool extensions of the Reqif Studio export either way. The only way to fix the problem I found so far was to completely replace the tool extensions of the Reqif Studio export with the original ones from the DNG export.
In case of not removing the tool extensions, does Reqif Studio do changes to them? As far as I understood are the tool extensions some sort of container which holds data which is outside the reqif specification.
Thank you for your effort.