Combine Files Not Working Acrobat Pro

I have been combining files in Acrobat for years, but it just stopped working. It goes through the process fine until it creates "portfolio 1", which is a list of files. But, when I hit "combine files" or "create file", that "new file" ONLY contains the first pdf -- not all of them. 

I have tried this when I select files from my computer; and also when I "select open files". Same thing happens. My creative cloud is up-to-date. What is  happening?