This is caused by the software that created your GEDCOM file.
It will have created names formatted as
1 NAME John Paul/Smith/ instead of
1 NAME John Paul /Smith/.
It would not be universally correct for kiwitrees to automatically add spaces because some languages (e.g. Chinese) do not use spaces between words or names.
But kiwitrees can insert insert these spaces for you. Go to Administration > Tools > Batch update and select the option “Fix name slashes and spaces”. If the tool finds any names that can be changed in this way it will display the first. You can choose to update these one at a time (being very cautious) or simply change all of them at once (being very confident).
As with most of the tools in the Batch Update suite, you should take a back-up copy of your latest GEDCOM file before proceeding.