This may be obvious to you but I cannot find the answer.
I am unable to get a , space between page numbers
Between Page Numbers Type or select a special character to separate one page number or range from another. The default is a comma followed by an en space.
Between Entries If Run-in is selected, type or select a special character to determine how entries and subentries are separated. If Nested is selected, this setting determines how two cross-references under a single entry are to be separated.
I've tried DEFAULT setting in another document, replacing, changing etc.
What version of InDesign and what OS are you? Did you try trashing preferences?