Copy & Paste Issues

Out of the blue I have been experiencing copy and paste issues on my 2012 iMac with 10.13.5. At times I am unable to use the shortcuts to perform copy and paste. At times I can use the Edit menu commands but not always. This happens in all apps. Yesterday I was able to copy a url but could only paste it into the subject line of an email and not in the text box.

I have killed the pboard several times. Still no luck.