Hi @jcosta46,
Unfortunately exactly the isBankHoliday(<offset>, <file>) action is broken in OH 2.5.x and will probably not working before OH 3.0 - even if it is already fixed in our code base (see Ephemeris: isBankHoliday(offset,filename) ignores filename · Issue #1374 · openhab/openhab-core · GitHub).
A small workaround is to use isBankHoliday(<datetime>, <file>) and set ZonedDateTime.now().plusDays(<offset>) for <datetime>.
I think we should add a note to the docs.