An element is being imported, but it is not on the timeline.
To begin with, try to apply the element, do not move/delete anything on the timeline until the element is applied (the progress bar will reach 100% and disappear signaling the application).
The elements may not be applied because the application may be blocked by antivirus/or firewall.
Try one or more solutions:
After the actions are completed, try to apply the element again.
You need to change access for Premiere Pro.
To change these preferences on your Mac, choose Apple menu > System Preferences, click Security & Privacy, then click Privacy > tab Accessibility.
Check the box for Adobe Premiere Pro of your version.
Now try again to apply the elements.
Also working on the Mac OS, you can see the following message (in different versions of the extension):
This can be fixed by enabling some options inside the extension.
Click to hamburger (3 mini lines) > Settings to open settings of the extension.
Check the box for these options:
GPU Supports &
Restart the extension and try to apply the transition again.