trying to remove a disabled bucket aggregation fails and can not be removed or re-enabled

[LeeDr]

Kibana version: 7.4.0, 7.4.2, 7.5.0

Elasticsearch version: 7.4.0, 7.4.2, 7.5.0

Server OS version: Cloud, Windows server,

Browser version: Chrome, IE11

Browser OS version: Windows 10

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

Describe the bug:

Steps to reproduce:

1. Create new vertical bar chart
2. Buckets > Add > x-axis > Terms > > Apply Buckets > Add > Split series > Terms > > Apply
3. disable that second Split series aggregation > Apply
4. click the X to remove that disabled aggregation - nothing happens. It isn't removed and you can't apply any change. You can't re-enable it.

Expected behavior: You should be able to remove a disabled aggregation.

Screenshots (if relevant):

Errors in browser console (if relevant):

Provide logs and/or server output (if relevant):

Any additional context:
I just tested the same steps in 7.2.1 in Cloud and in that version I can delete a disabled aggregation.

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)

[LeeDr]

I just tested these steps on 7.3.2 in Cloud and it works there too. So it appears to be a regression from 7.3 to 7.4.

[sulemanof]

The issue is not reproducible on master.
Tested on Windows in Chrome & Firefox
Stable working at least from 7.6.