As I was exploring the latest version of the snapshot I began to notice around water logged caves that Mineshafts were not generating properly they were left with a small amount of only 5-10 blocks long of the actual structure sometimes there was a mineshaft near by but other times not one in site. I thought it might of just been the one seed with some strange generation as can happen so I decided to see if I could find it in another, which I did. I also tried to use /locate mineshaft when I was near a water logged cave and it would teleport me to where a mineshaft wasn't.

I didn't get the seed of the first world as I accidently deleted it while trying to clean out my worlds but did get the other world seed: -8129799347996775707

In image 2 you can see that there was parts of another mineshaft close by but the too were disconnected.