If you create a new Custom Event and then delete it you can’t use the same name in variables/functions etc. Reproduced in a blank project, Engine Version 4.7
Steps to reproduce this bug:
Create a new custom event
Set any name to this event
Delete this custom event
Try to create a variable or a function with the same name…
Have you updated to 4.8.0 or are you on a preview build? I’ve attempted this on my end following along with the video however when I rename either functions or variables after creating and deleting a custom event it seems to work as intended. I’ve also tried compiling between steps to see if that caused the error, however it did not seem to make a difference.
I noticed that the problem can be somewhat solved by adding a new custom event and giving it a different name, then deleting it. (It unlocks the name, but locks the new one, so it’s not a permanent solution.)
I made an another video to show what i am exactly doing:
I get “test is in use by another variable or function!”
While I could not reproduce it myself, this is clearly occurring in your videos. I have attached the second video you posted along with the information here to a bug report, UE-17225, to be assessed by the development staff.
You have to search for it within the side panel and delete it there then it will allow you to create a new event with the same name. In the image, you will search for the name and then right-click and delete it from the menu. Hope this helps