Nikos,
Thanks for the update!
You mention Write Mode: which types of work can you do in Write Mode without playing your score? Generally, it seems as though this is a bug which appears only when Playing. Maybe that’s what you’re saying?
Please would you add your findings to this thread so as to let Paul at Steinberg know that way exactly what your system configuration is like this - to help him identify possible causes.
Thanks and good luck!