Ok, I have reported issue 4 days ago and today received message from Shandryn:
[QQ]Players have been unable to interact with the chest in the Sludge Fen of the Barrens for approximately the last 4 days. (12/9/2016 is approximately when I first saw it) A GM of sufficient rank should be able to mark it complete for you as long as you are online and provide proof that you have the 2nd half from Silverpine forest. Until it's fixed, please submit a ticket and show that you have the other half in a screenshot.
I suspect it will be resolved upon a server reboot, but I wanted to add this note in case anyone comes looking.
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