I was having problems with the new Quick Add package that I created after we updated to Jamf Pro 10.4. It seems that there is a bug in the Scripts>postinstall script.
I had to open the newly created Quickadd package in Composer
Scripts>postinstall scroll down to the "Use the correct binary for the os version," There is a command line missing - in my QuickAdd it is line 54. I have attached a screen shot /bin/mkdir -p /usr/local/bin
Once that command was entered, and the QuickAdd was saved, I was back in business.
I hope this helps others!