Script can be saved with Project -> Save. No need to copy script content from script tab.
The code runs too fast on the page unless I restart your software.
I can't reproduce that.
Click on the next button is disabled. Change mode to "Execute and add"
You told that Is Exists is not working, but I don't see any "Is element exists" action on your side.
You need to do something like this
0_1496325530607_CheckExists.png
Because there are pages which is deleted by author and there is no reply button.
I also have problems with using coordinates, but when I cahnge selector >CSS> :nth-child(1) > p > .reply-email which is default, it works fine for more. Why do you desided to change selector from default?
You don't need to call Wait Full Page Load every time. Just click here
0_1496325669806_WaitFullPageLoad.png