When we first tried these disks they were incorrectly labeled. The disk was labeled "14" was actually a "16." The results were cracked units just like yours. The initial plunge into the wax disk damages the millable area and it cracks later in the milling process.
Other issues might be a dirty collet or loose collet.
why is a smaller connector so desireable? Either way I have to cut it off and flatten it. It is so easy to do that I don't really see the advantage to push the envelope to make it thinner. 2 mm is my default setting.