[8.15] [Observability] [Alerts table] Fix cannot display alerts error (…

…#198914) (#198938)

# Backport

This will backport the following commits from `main` to `8.15`:
- [[Observability] [Alerts table] Fix cannot display alerts error
(#198914)](#198914)

<!--- Backport version: 9.4.3 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sqren/backport)

<!--BACKPORT [{"author":{"name":"Bena
Kansara","email":"[email protected]"},"sourceCommit":{"committedDate":"2024-11-05T12:57:32Z","message":"[Observability]
[Alerts table] Fix cannot display alerts error (#198914)\n\nResolves
https://github.com/elastic/kibana/issues/198912\r\n\r\n### Testing\r\n-
Create ES query rule in Observability\r\n- Open Alert flyout of the ES
query alert\r\n- Verify that Alert flyout opens as
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[Alerts table] Fix cannot display alerts
error","number":198914,"url":"https://github.com/elastic/kibana/pull/198914","mergeCommit":{"message":"[Observability]
[Alerts table] Fix cannot display alerts error (#198914)\n\nResolves
https://github.com/elastic/kibana/issues/198912\r\n\r\n### Testing\r\n-
Create ES query rule in Observability\r\n- Open Alert flyout of the ES
query alert\r\n- Verify that Alert flyout opens as
expected","sha":"f8c01d41d2dc6c4c4d096c485b48dc7decafd873"}},"sourceBranch":"main","suggestedTargetBranches":["8.16","8.x","8.15"],"targetPullRequestStates":[{"branch":"main","label":"v9.0.0","branchLabelMappingKey":"^v9.0.0$","isSourceBranch":true,"state":"MERGED","url":"https://github.com/elastic/kibana/pull/198914","number":198914,"mergeCommit":{"message":"[Observability]
[Alerts table] Fix cannot display alerts error (#198914)\n\nResolves
https://github.com/elastic/kibana/issues/198912\r\n\r\n### Testing\r\n-
Create ES query rule in Observability\r\n- Open Alert flyout of the ES
query alert\r\n- Verify that Alert flyout opens as
expected","sha":"f8c01d41d2dc6c4c4d096c485b48dc7decafd873"}},{"branch":"8.16","label":"v8.16.0","branchLabelMappingKey":"^v(\\d+).(\\d+).\\d+$","isSourceBranch":false,"state":"NOT_CREATED"},{"branch":"8.x","label":"v8.17.0","branchLabelMappingKey":"^v8.17.0$","isSourceBranch":false,"state":"NOT_CREATED"},{"branch":"8.15","label":"v8.15.4","branchLabelMappingKey":"^v(\\d+).(\\d+).\\d+$","isSourceBranch":false,"state":"NOT_CREATED"}]}]
BACKPORT-->

Co-authored-by: Bena Kansara <[email protected]>

x-pack/plugins/observability_solution/observability/public/components/alert_overview/helpers/map_rules_params_with_flyout.ts

@@ -269,7 +269,7 @@ export const mapRuleParamsWithFlyout = (alert: TopAlert): FlyoutThresholdData[]
       const { thresholdComparator, threshold } = ruleParams as EsQueryRuleParams;
       const ESQueryFlyoutMap = {
         observedValue: [alert.fields[ALERT_EVALUATION_VALUE]],
-        threshold: threshold.join(' AND '),
+        threshold: [threshold].flat().join(' AND '),
         comparator: thresholdComparator,
         pctAboveThreshold: getPctAboveThreshold(
           threshold,