Logstash 5.4.0 - Concatenate fields in Logstash csv filter stopped working

[RedCloudDC]

I have separate fields for lat and long values and use logstash to csv filter combine the fields then an index template to convert them to a geo_point. This line WORKS in Logstash 5.3.0

add_field => {"from_location" => "%{Latitude},%{Longitude}"}
}

with no changes, this line does not work in 5.4.0 (see parse error below). Do I need to do something different in Logstash 5.4.0?

:response=>{"index"=>{"_index"=>"idb_csvparsefailure", "_type"=>"parse_failure", "_id"=>"AVyeFR3faPgK4Al0Wt9r", "status"=>400, "error"=>{"type"=>"mapper_parsing_exception", "reason"=>"failed to parse", "caused_by"=>{"type"=>"number_format_exception", "reason"=>"For input string: "{%Latitude}""}}}}}