Word for someone who is an incompetent intermediary?

I'm looking for a single word that would be used to describe someone who is an incompetent intermediary. To be more specific I would like to describe someone whom it is necessary to communicate knowledge through, however this person doesn't have the proper skill set to understand or further communicate the knowledge accurately and effectively.

As a hypothetical example, consider a scenario where an engineer communicates technical knowledge with a program manager, who then attempts to communicate that knowledge with a customer. However, because the program manager lacks technical prowess, the relayed message is distorted to the point being mostly or completely wrong. What word would one use to describe the program manager? Preferably I would like to find a non-pejorative term.

Edit I would also be interested in any phrases that describe such a person.

Solution 1:

I would describe them as a stumbling block.

The second definition is:

an impediment to belief or understanding

which sounds exactly like your hypothetical programme manager.

It also has the benefit of sounding less derogatory than synonyms like hindrance, impediment or obstacle.

Solution 2:

You could use weak link:

The least dependable member of a group, as in The shipping department, slow in getting out orders, is our weak link in customer service, or They're all very capable designers except for Ron, who is clearly the weak link. This expression alludes to the fragile portion of a chain, where it is most likely to break.
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Although its idiomatic usage does not actually imply an intermediary, it fits nicely with your usage because links connect things together.