A few months ago the automatically relist 3 times for free box disappeared, so I contacted eBay about it. They said that it is probably because I had sold over 100 items. They also suggested I clear my browser cache as that can sometimes affect it. I cleared out and the box returned. I wondered then if I was on borrowed time having sold over 100 items, but so far I have no lost that box again.

So, I would assume that selling over 100 items can cause you to lose the option to relist for free. It may have just been a general cut and paste reply too and they were completely off track.