The query exists:fieldname doesn't work in Kibana, when querying via search bar, but works with filter UI ("Add a filter" button).
The query created in the first case:
...
"filter":[{
"bool":{
"should":[{"match":{"exists":"pagetype"}}]
}}]
...
The query generated for the second case:
...
"exists":{"field":"pagetype"}
...
P.S. This editor removes underscore character before and after the exists, so know it's there