Issue Summary

BulkPageCopyTaskRunner aborts the entire copy operation when the source page (or any page in a copied tree) carries a content restriction (Edit or View) for a group that no longer exists. 
The end-user only sees a generic UI error: "An error occurs. Please try again later." — with no indication that a stale group restriction is the cause. A single orphaned restriction also aborts an entire page bulk copy.

Steps to Reproduce

 In a Confluence Cloud site, identify (or create) a page that has an Edit or View restriction assigned to a group, then delete that group so the content_perm row becomes orphaned 

• As any user with copy permission, open the affected page → ••• → Copy page (or Copy page tree for bulk).
• Choose any destination space/parent, leave Copy Permissions / Restrictions ticked.
  Click Copy.

Expected Results

•  The copy succeeds.
•  Orphaned content restrictions referencing deleted/non-resolvable principals are gracefully skipped (and ideally logged/surfaced) rather than aborting the entire copy task.
•  For bulk copy, one bad page should not abort the remaining pages.

Actual Results

UI shows: "An error occurs. Please try again later."
•  Single-page copy fails outright; bulk page-tree copy aborts mid-task.
•  No actionable detail is shown to the end user.

Workaround

For single-page copy: an admin must remove the stale content restriction from the source page before the copy will succeed.
For bulk page-tree copy: in the Copy Page dialog, untick "Restrictions" / "Copy Permissions" before clicking Copy. The destination pages will then inherit space/parent restrictions instead.