The forecast.weather.gov/MapClick uses data from internal(NWS) sources, the advforecast2 V5 script uses the data from api.weather.gov.
Sometimes, the API and the internal(NWS) sources do not match due to internal NWS data sync issues. Since they took down the forecast-v3 site (which used the API, there's no longer a good way to show that the differences exist due to internal NWS issues.
The check-fetch-times.php?show=versions will always use the V5 script as the 'latest'. The V4 script hasn't been updated since V4.05 - 21-May-2018 , but since the forecast.weather.gov site has remained the same, the script still works just fine.
Yes, reverting to the advforecast2 V4 script would keep your site in total sync with what forecast.weather.gov/MapClick says.
And yes to what Jasiu says.. PHP 5.4 has been 'gone' a long time. Best to use PHP 7.2+ (I'm using 7.4.1)