Something is causing the bold dates to not parse correctly. The bold marks these as invalid date formats. The date column width may be too narrow to show the problem data.
Double-click one of those rows of records to bring up the editor. (The date field that was bold in the table-style view should be red in this form-style dialog.)
It may be that the affected date has some text appended that cannot be parsed.
As an example “12 July 1868 approx.” would not be parsable. It would have to be changed to something like “about 12 July 1868”. You could use “abt”, “circa”, “c.”, “~” instead of “about” too.)