The problem is in your splash property:
The clue which tipped me off was the error message in the log, which hinted that the project’s resources might have a problem:
2020-12-20 10:50:33,121 - root - ERROR - An exception has occurred!
Traceback (most recent call last):
File "shutil.py", line 788, in move
FileNotFoundError: [Errno 2] No such file or directory: '/Users/george/Downloads/BS7909TempInstallCerts.appstudio/voltbuilder/www/resources' -> '/Users/george/Downloads/BS7909TempInstallCerts.appstudio/voltbuilder/resources'