'Collections is temporarily unavailable' error message on UI

Issue

• When a collection uses a web content structure that has been deleted, the error 'Collections is temporarily unavailable' appears.
  Steps to Reproduce:
  1) Navigate to Site > Content & Data > Web Content > Structures
  2) Create a simple structure 'structure1'
  3) Navigate to Site > Site Builder > Collections
  4) Create a dynamic collection
  Set source to:
  Item type = Web Content Article
  Item subtype = 'structure1'
  5) Save collection
  6) Navigate to Site > Content & Data > Web Content > Structures
  7) Delete structure 'structure1'
  8) Navigate to Site > Site Builder > Collections
  Observed Behavior: Collections is temporarily unavailable.
  Expected Behavior: Collections overview should appear.

Environment

• Liferay DXP 7.3

Resolution

• The observed behavior is a known Liferay DXP bug which has been addressed in Liferay DXP 7.3 SP4
• If the hotfix is required for this issue, please create a support ticket requesting the hotfix by attaching the patch details.
• Installing Fix Packs and Hotfixes on Liferay DXP will guide to installation of the hotfix in the respective environment.

Additional Information

• LPS-125486

• Starting from Liferay DXP 7.3 SP4, DXP 7.3 releases will be called Updates rather than fix packs or services packs. Updates are still cumulative and will contain the same types of changes: bug fixes and limited new features. 
  For more about Liferay's patching strategy please see: Liferay Patching Overview.