Try going to Edit > Device Setup and in there change to a different sample rate, wait a few seconds and switch back to the previous. Close the dialog and try playback again.
If it still does not work, please do Help > Create Diagnostic Report. That creates a zip file on your desktop. Please attach here.
Would be also good if we could get hands on the project. If you don’t want to post it here publicly, you could send it to ‘u dot stoermer at steinberg dot de’. Confidentiality fully guaranteed.