Same question.  I switched mine to use $map so it theory it should work.  But I just get blank.
if ($feature.EvalStatus == "Eval") {
var sql = "PlotKey = '" + $feature.PlotKey + "'";
var tbl = Filter(FeatureSetByName($map,"GAP"), sql);
var txt = ''
for (var f in OrderBy(tbl,"LineKey")) {
    txt = txt + Right(f.LineKey,1) + '-'
}
txt = Left(txt,Count(txt)-1)
if (txt != '1-2-3') {
    return "\nLine Number Issue! Found: " + txt
}
else {
    return ''
}
}
else {
    return ''
}
Thanks