The marriage date that is shown in Changes to People You Follow is being abbreviated from the actual date in the person page.
Please change the marriage date to the full date in the people you follow section.
The system did not truncate the date. There were multiples of the same marriage event attached to the couple - one with a short-form date and one with a long-form date. The one that was deleted had the short-form date.
The dates shown in Family Tree in general are what the last editor actually entered. The editor can choose to enter dates in a variety of formats, which may or may not correspond to the standardized (full date).
The examples you showed in your screen shots are for Samuel Henry Miller and Virginia C. Wright.