Search on stale index breaks Search Portlet UI when category was deleted and remote search server departs

• Type: Bug
• Status: Closed
• Resolution: Fixed
• Affects Version/s: 6.2.5 CE GA6, 6.2.10 EE GA1, 7.0.1 CE GA2, Master
• Fix Version/s: 6.2.X EE, 7.0.0 DXP FP1, 7.0.2 CE GA3, 7.0.0 DXP SP1, 7.0.3 CE GA4, 7.1.X, Master
• Component/s: Web Search > Search Widgets
• Labels:
  • ee-ts
  • liferay-digital-enterprise-70-sp1
  • liferay-fixpack-de-1-7010
  • liferay-fixpack-portal-119-6210
• Branch Version/s:
  7.0.x, 6.2.x
• Backported to Branch:
  Committed
• Story Points: 1.25
• Fix Priority: 3
• Git Pull Request: https://github.com/brianchandotcom/liferay-portal/pull/41792

1- Configure Liferay to connect to a REMOTE search server (7.0/DXP: Elasticsearch or Solr, 6.2: Solr)
2- Create a category
3- Create a web content and use this category
4- Disconnect the search server (simulate an outage)
5- Delete the category
6- Re-connect the search server
(7- 6.2: Add Search Portlet to a page)
8- Search for "test"
(9- Click on the name of the category on the left facet panel)

Result: page (UI) is broken. See the screenshots attached
Expected Result UI remains "coherent" and does not get broken

See the comments below for more information about the setup and other.