DateDiff returns one month less than it should when comparing dates that are at the end of the month, if the months in these dates have a different number of days. An example will explain this better:
ACF returns 3 in this case. That is the correct behaviour.
Ubuntu. I haven't been able to test on a more recent version. However, the last commit is from 2015, so I think it's safe to assume that all Lucee versions have this bug.
I've added testcase for this ticket & confirmed that issue happened.In lucee, for dateDiff function while taking month as datePart it differs from ACF. ACF working as expected but Lucee didn't.
Pull request: https://github.com/lucee/Lucee/pull/175