I have also experienced the spinning wheel of "hang on your gonna have to wait a minute" for quite a few operations, and indeed is random.
I have to say after using it for an evening of editing some artwork images, all vector no pixel layers. I got feed up and opened the same file in a back up of the previous release of designer. I had no problems or spinning wheels and didn't have time to notice any of the new features in the up-date. So not missing any of them as of yet.
Perhaps when there is a future up-date I will see if I experience the same lag and spinning wheel of death....
Just my experience sp far with the new 1.8.4 release, other than that I love the software.!
Cheers dopeNL.
macOS Mojave (by the way,)