Don't know why but Cura is no longer able to connect to my printer.
I upgraded form 4.0 to 4.1, using a wireless LAN to connect to Octoprint 1.3.11, running a Creality CR-10 3D Printer. I had no issues with Cura 4.0, only with 4.1 release. I downgraded back to 4.0 and I can connect to my printer without issue.