[BUG] Filters saved in Saved Searches cannot be loaded

[gordon-chen-aiven]

Steps to reproduce:

1. Goto "Discover", add a filter and save the search.
2. Click “Open” then the search directly to open it, the filter is present in the opened search
3. Click “Open” then “Manage searches”, it goes to “Dashboards Management → Saved objects”
4. Inspect the saved search and the filter is present.
5. Go back to “Dashboards Management → Saved objects” and click the search to open it, and the filter is disappeared.
6. The filter will never show up again afterwards no matter how it is opened, but the filter is still in the search if you inspect the search.