[TSVB] request with Filter Ratio failed, ES response is Unknown key for a START_OBJECT in [[object Object]]

[tsullivan]

Kibana version: 7.9.1

Elasticsearch version: 7.9.1

Server OS version: Linux

Browser version: Chrome 86

Browser OS version: Linux

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

Describe the bug:
TSVB panel fails for some mysterious reason. All network requests in developer tools show 200 responses, but an ES error is buried inside. No other indication of the error shows in the browser.

Steps to reproduce:

1. Create a line chart on data in the Time Series panel
2. Switch to Table panel and select a field to group by
3. Add a column
   • Aggregation: Filter Ratio
   • Metric: Sum
   • Field: some numeric field

Expected behavior:
Should show the table and column with the filter ratios

What actually happens is the panel becomes this:

The screen shows no feedback to the user about the failed request.

Network Inspector shows all requests receive a 200 response. Here is a sample response:

{"type":"table","uiRestrictions":{"whiteListedMetrics":{"*":true},"whiteListedGroupByFields":{"*":true},"whiteListedTimerangeModes":{"*":true}},"61ca57f0-469d-11e7-af02-69e470af7417":{"id":"61ca57f0-469d-11e7-af02-69e470af7417","statusCode":400,"error":{"error":{"root_cause":[{"type":"parsing_exception","reason":"Unknown key for a START_OBJECT in [[object Object]].","line":1,"col":1266}],"type":"parsing_exception","reason":"Unknown key for a START_OBJECT in [[object Object]].","line":1,"col":1266},"status":400},"series":[]}}

The part about [object Object] looks as though some data is not serialized properly for the query to ES.

Screenshots (if relevant):

Errors in browser console (if relevant):

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

Any additional context:

[elasticmachine]

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

[RicoNijeboer]

I am getting the same error on 7.9.3

Kibana version: 7.9.3

Elasticsearch version: 7.9.3

Server: Elastic cloud

[DianaDerevyankina]

Seems that this issue has already been reported earlier in #65849 and was fixed by #77272 that's why it's not reproducible since 7.10.
As it's still relevant for 7.9, @timroes @stratoula I'd like to know if we need to backport.

[stratoula]

As we don't have any 7.9.x release planned and the bug is fixed on 7.10 I think we should not backport it. For this reason, I will close this issue cc @dziyanadzeraviankina