I suffered this problem some time ago: once and only once and I have never been able to duplicate the problem.
In case anyone is curious, this was the story:
I had a brand new C drive onto which I loaded Linux Mint.
After poking around with that OS for a little while I downloaded the then new Kicad 5.1.9.
Next I checked that I could find and open my Kicad circuit files that live on D drive.
Next I started a new project. Then a new personal global library.
Then: Open symbol editor
Edit part and rename from Kicad library.
Save to my new library.
Open new part in my new library.
Edit aliases: deleted about 10 aliases.
Click OK then complete Kicad crash.
Second attempt, same result.
Checked new library to make sure no typos in the path.
Third attempt I only deleted one alias. Kicad thought about this for about two seconds then deleted the one alias.
Fourth attempt I deleted the other nine aliases and the programme worked properly, instantly and has never faulted since.
Spent a good hour yesterday trying everything I could think of to help the OP but just couldn’t repeat the fault.