Catch dog stopped catching?

Interesting. A dog that prefers to catch on the snout and will catch big pigs but won't catch consistently.
One simple test I would do if I was you since your partial to the dog . Work with the dog by himself without the presence of any other dogs. Where the dog can't hear or see other dogs. Introduce the dog to a decent pig, say 200 pounds. If the dog won't straight up catch, you most likely don't have a catch dog, just a real rough gritty dog. If you would like to explore that more, on a different session, put two rougher type bay dogs in a bay pen with the same pig. Let them bay him and let the dog in question listen for a minute and watch and then allow it in the pen. Same outcome or different now?
Exceptions:
Is the dog is young, it could be that the dog is in sensory overload at times and will grow out of that.
Are the times the dog won't catch, only the times when multiple hogs are bayed up at once?
If any of these two are yes, the bay pen won't tell you much beyond what the answere to the two questions did. The bay pen will be a good place to work with the dog though, just remove the bay dogs and start with smaller pigs and work up in size. If the answere to both questions are both no, it could very well be something the dog is reading and picking up from you given the circumstances you previously mentioned. I'm not gonna go into explaining this, most people won't comprehend it and it would be pretty lengthy to explain. If both those questions are no, just much much easier on you to get a different catch dog, one that's full AB or pit. Hard to go wrong with either of those, though there will always be an exemption here and there.