There might be various issues of the 419 what we have encountered till now would be documented here.
Extra space in some files after closure of ?> php tag
The easy way to find is when you run any laravel command you will see that space when laravel echo success message as in below case.
Space in Laravel command
Finding the space is bit time consuming but mostly it will be in one of the file written by coder so focus on files which are coded rather than laravel files.
No Space in Laravel command
After this the there was no 419 error