During the ascension, when one of the human shaped balls would get hit by the wooden blocks, that is when the game crashes.
Viewing post in Humanity Clicker 1.4.3 WEB comments
ok I do believe I found the issue. There were two script errors there that I fixed.
The next update is nearly done, It will come out probably tomorrow, bringing the fix to it. Don't worry though your save will still work(but you might want to make an account to upload it to the cloud to make sure its not lost once the file is updated)