var applicationsPipeline = PipelineDefinition<AffiliateRecord, List<ApplicationRecord>>.Create(new IPipelineStageDefinition[] {
    PipelineStageDefinitionBuilder.Match<AffiliateRecord>(filter),
    PipelineStageDefinitionBuilder.Unwind<AffiliateRecord, AffiliateRecord>("Applications"),
    PipelineStageDefinitionBuilder.Match<AffiliateRecord>(matchApplications),
    PipelineStageDefinitionBuilder.ReplaceRoot<AffiliateRecord, List<ApplicationRecord>>(x => x.Applications),
    PipelineStageDefinitionBuilder.Skip<List<ApplicationRecord>>(offset),
    PipelineStageDefinitionBuilder.Limit<List<ApplicationRecord>>(limit),
});

var applicationsFacet = AggregateFacet.Create("applications", applicationsPipeline);

var aggregate = collection
    .Aggregate()
    .Facet(applicationsFacet, ...);

var facetResult = await aggregate.SingleOrDefaultAsync();

System.FormatException: Cannot deserialize a 'List<ApplicationRecord>' from BsonType 'Document'.