I'm having the same trouble with felted wool covers. I take very good care of them, but I guess I'm unlucky....I've had 2 with holes now. The hole develops right behind an outermost snap. The wahm replaced the first of my covers with a hole for me with one with reinforced snaps, no problem. She then also sent 2 more reinforced covers just in case the 2 other non-reinforced covers I had left developed problems. Just in case. Wonderful customer service from her. But now one of the replacement reinforced covers is developing a hole in the exact same place. What a bummer. I'll let the wahm know, but I don't know how many times I can reasonably expect her to replace a cover.
Makes you think that maybe aplix is the answer instead of snaps with wool? Seems like it would put less stress on the fabric? Maybe I'm wrong. I was thinking that perhaps the felted wool just isn't always thick enough to handle the stress, but with your post, it looks like the problem happens with jersey as well. I wonder how prevalent the problem is with wool and snaps?
I figure it's in everyone's best interest to let manufacturers/wahms know when you have a product of their's that doesn't perform up to snuff. How else will the manufacturer know they've got a problem? And it gives the manufacturer a chance to build better relationships with their customers.