Dorico 4 Crashing (or so it seems)

Would I be correct in guessing that you had selected a bar or similar by clicking in a blank part of the staff, and then tried to paste your playing technique? If so, then you’re experiencing this crash:

For the time being, make sure that you select only a single note or chord as the destination for your paste, and you should find that it works OK. Sorry for the inconvenience caused: this will be fixed in the next update.