Dynamic Percentile lines in scatter plot visual not working with month slicer

The core reason the month slicer has no effect is that Grid3 is a calculated column. A calculated column is evaluated once, at data refresh, in a fixed (no-slicer) context - it physically stores one value per row and can't react to a slicer at report time. So whatever the month slicer does, every row keeps the Grid it was assigned at refresh.

On top of that, your feeder measures use ALLEXCEPT('agg_route_trip','agg_route_trip'[service]), which removes the filter from every column except service - including the month column - so even the measure logic is ignoring the month context.

To make it react to the month slicer:

1) Make the percentile thresholds (and the reference lines) measures, so they recalculate under the current month filter, e.g. wrap your PERCENTILEX.INC over SummaryTableX/Y in measures rather than baking them into a column.

2) Fix the feeder measures so they don't ALLEXCEPT the month away - keep the month/date in context (use REMOVEFILTERS only on the columns you actually need to clear, not the whole table).

One honest caveat: a scatter plot needs a column for the point grouping/Details, and a column can't be slicer-aware. So if you specifically need each point re-assigned to a different grid when the month changes, build SummaryTableX/Y at service + month grain (so "service in July" is its own row) and slice on that. That gives you month-reactive points plus measure-based percentile lines - which is something a single calculated column can't do by design.