Okay, I've confirmed that the offline area doesn't appear to download my hosted table, and this is why the calculation fails. I tried using a point FS with records added to attribute table and no actual point geometry (appended my table to the host point feature layer). This also doesn't work; I believe the offline map is not downloading the records needed for filter() function.
The only way I can see that this seems to work is if I have a feature within the download area that gets downloaded and can be used as lookup record.
So my workaroud will be to try and create a polyline or polygon FL that contains a bunch identical features which span across the state of Washington and will be captured by any one of the offline areas our surveyors might use. Feature attributes will contain my lookup data. This is insanely messy...
If anybody has a better solution, I'd love to hear it. or if @JeffShaner and team can help with this bug (ENH-000157471), I think a lot of people could benefit.
Thanks!