If it is the 2.12.3.11 hotfix no need to ask for it. We tested it on our managers but still see this specific error message popping up.
We are now running 2.12.3.11 agent (which works quite well just not with all 2.9 appstacks) and 2.12.1.103 manager. For me it seems to be the most stable and quickest combination until now. And believe me I have seen a few 
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