Warning text doesn't get displayed on filters with custom filter name

[bhavyarm]

Kibana version: 7.9.0 BC6

Elasticsearch version: 7.9.0 BC6

Server OS version: darwin_86_64

Browser version: chrome latest

Browser OS version: OS X

Original install method (e.g. download page, yum, from source, etc.): from staging

Describe the bug: If user has a custom label on filters and switches index pattern for which the filter is not applicable - warning text about field does not exist in the current view doesn't get displayed.

Steps to reproduce:

1. Have two index patterns -> Go to discover - create a filter on a selected index pattern and give it custom label
2. Switch the index pattern to another
3. Kibana doesn't display the warning label as it does if there was no custom filter label

Screenshots (if relevant):
Warning getting displayed on filters without custom label

No warning on filters with custom label

[elasticmachine]

Pinging @elastic/kibana-app-arch (Team:AppArch)