Logstash Grok Pattern, mutate - logstash-grok

Question

i ran into a problem.
i have a pipeline:
input {
tcp {
host => "10.10.10.10"
port => "5959"
codec => "json"
type => "my_type"
mode => "server"
}
}
filter {
if [type] == "my_type" {
grok {
match => {"message" => ['\#%{GREEDYDATA:who}%{SPACE}#%{GREEDYDATA:what}\n\n%{GREEDYDATA}: %{GREEDYDATA:contact}%{SPACE} #%{GREEDYDATA:ident}\n%{GREEDYDATA}Cost:%{SPACE}%{DATA:cost}\n%{GREEDYDATA}Date:%{SPACE}%{DATE_EU:when}\n%{GREEDYDATA}Vacant:%{SPACE}%{DATA:vacant}\n(?<info>(.|\r|\n)*)\n\[%{GREEDYDATA}']
}
}
mutate {
gsub => [
"what", "milkshake", "Milk 🥛",
"what", "icecream", "Ice 🍦"
]
}
mutate {
gsub => [
"cost", "-1", "?",
"contact", "9", "+9"
]
}
mutate {
gsub => [
"contact", "\+9", "tel:+9"
]
}
if [date] {
date {
match => [ "date", "ISO8601", "YYYY-MM-dd'T'HH:mm:ss.ZZZ" ]
target => "#timestamp"
} }
if "_grokparsefailure" in [tags] {
drop {}
}
}
}
output {
if [type] == "my_type" {
elasticsearch {
hosts => ["https://localhost:9200"]
index => "my_type-%{+xxxx.ww}"
ilm_rollover_alias => "my_type"
ilm_policy => "my_type"
ilm_enabled => "true"
cacert => ["/etc/logstash/ca.crt"]
user => "elastic"
password => "password"
}
}
}
in the mutate section after the GROK i replace one word with another which will contain emoji and be capitalized
mutate {
gsub => [
"what", "milkshake", "Milk 🥛",
"what", "icecream", "Ice 🍦"
]
}
but in elasticsearch in the "what" field I see that the word is substituted with a non-capital letter "milk 🥛" instead of "Milk 🥛"
I tried to force mutate for the capital letter, but that doesn't help either ("mutate" for the capital letter was placed after the "mutate" for replacement)
mutate {
capitalize => [ "what" ]
}
What can be wrong?