NaN passes the value.numeric() check in WindowFunctionPercentileCommon::add and inserted into boost::container::flat_multiset<double>. NaN violates strict weak ordering (NaN<x and x<NaN are both false), so the multiset's binary-search invariants gets corrupted; subsequent remove() calls can erase the wrong element and downstream getValue/remove either return wrong percentiles or trip tassert 7455904. Filter NaN in add/remove the same way AccuratePercentile::incorporate does for the non-window accumulator.