Delirium Quest Stuck (4/5 Bosses) - 5th Boss Missing, Progression Blocked

My Delirium quest progression appears to be permanently blocked due to one of the required Delirium quest boss encounters becoming unavailable while the Atlas node was still marked as completed.

Issue:

The Delirium questline requires killing five designated Delirious Map Bosses in order to continue progression with Elder Madox and unlock further Delirium progression.

I successfully completed four of the five required Delirium quest bosses.

On the fifth designated Delirium boss map, the encounter bugged and I was unable to kill the boss. Despite the boss not being killed, the Atlas node was subsequently marked as completed.

The problem is that the node cannot be replayed and the quest boss cannot be respawned.

Current State:

Four Delirium quest bosses completed successfully.
Fifth Delirium quest boss was not killed due to a bugged encounter.
The Atlas node for that encounter now shows as completed.
The boss is no longer available.
The node cannot be replayed.
No replacement Delirium quest boss has spawned elsewhere.
Progression with Elder Madox is blocked.
Delirium progression cannot continue.
Delirium passive tree progression is blocked.
Amulet anointing remains unavailable because the Delirium questline cannot be completed.

Troubleshooting Already Attempted:

Restarted the game multiple times.
Restarted after recent hotfixes.
Continued mapping in surrounding Atlas regions.
Completed additional Delirium maps.
Used Boss Tablets to attempt to generate additional Delirium boss encounters.
Checked whether additional Delirium bosses would count toward quest progression.
Progressed other Atlas content.

None of these actions restored the missing quest boss or allowed the quest to continue.

Additional Concern:

Atlas progression is account-wide. Creating a new character does not appear to resolve the issue because the same Atlas state is shared.

Expected Behaviour:

If a required Delirium quest boss is not successfully killed, one of the following should occur:

The encounter should remain available until completed.
The Atlas node should not be marked complete.
The boss should respawn when the node is replayed.
A replacement quest boss should be generated.
The quest state should recover automatically after a restart or patch.

Actual Behaviour:

The required quest boss is gone, the Atlas node is completed, and there is currently no way to finish the fifth Delirium quest boss requirement.

Result:

Delirium progression appears permanently blocked on the account.

Attached Screenshot:

Screenshot attached showing:

Completed Delirium quest nodes.
Missing/inaccessible fifth quest boss encounter.
Current Atlas state demonstrating progression blockage.
Screenshot:
https://imgur.com/a/poe2-deli-quest-4-5-bosses-killed-cOm5jvN