Document Splitter not finishing naming of book file

I'm able to use the Doc Splitter in Fm 2022, roughly equivalent to the Fm 2020 version. 

However, the process hangs up before producing a book name with a valid name.

In otherwords, instead of getting ProjectName.book, I'm given ProjectName.txt.

I can quickly give the file the proper extension, but I feel like there's something I'm missing that is halting the process prior to delivering the .book.

Anyone else see or solve this?

-Matt