Unique Strongbox instance disconnect

Started a Unique Strongbox Kirac mission in Spider Forest map scaled to Tier 8. Identifying the strongbox (not opening) caused a disconnect, followed by Failed to connect to Instance for a few minutes after attempting a log in again on the same character, or any alternate character if teleporting to the Hideout.
After successfully logging in and returning to the map instance, approaching the strongbox again (i.e. having it in render distance) caused another Unexpected disconnect & failed to connect event.
I do have the Tamper-Proof and Secret Operations Atlas passives if that matters.

Essentially that Map instance is now softlocked, as the strongbox is on the way to the boss and the Mission objective. A shame.