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Piehead, is the instaled cable part of the building infrastructure? What length is it ( it can be checked with a CAT5 Cable tester in situ (Fluke micro scanner or equivelent type)).
My experience is this is usually the cheapest possible cable usually installed with very little care, I have the same system you describe of using patch cables to attach to drums and this seems to work quite well though I do use Neutrik Etherflex cable on the drums and Stix is quite correct there is a list of reccomended cables for use (on the A&H website) for use with both ACE and Ethersound.
I too would connect the surface to the rack directly as a test first, I would also be tempted to install a dedicated link using good quality carefully installed cable, I would suggest you use cable designed for “deployable use” like Etherflex, CAT Snake, Tour CAT this may seem a little excessive but tour grade cable usually is more forgiving sadly also more expensive.