Workflow Date Calculation

I have an instance of SuiteCRM where date calculations are not working (event setting one date field equal to another).

I have two other installations on the same version, with the same workflows on another server that work no problem.

Looking for ideas:

PHP version? Are there specific PHP extensions that would handle dates that I should look for?

Any other troubleshooting ideas? I’ve tried formatting the dates about a million different ways, exactly like in the documentation. If I set the date in the date calc it works, if I use a field value I get either a NULL value or 1969 value.

So as a followup, I still can’t figure it out but what I did was create another field for “created date” and made it equal to “date created” then used my custom “created date” field in the calculation. Still can’t figure out why I can’t use the default date created. And it’s only on this installation!