The newest skins for Blitzcrank have taken a leave of absence from the League of Legends store until the next patch releases.
Lancer Paragon Blitzcrank and Lancer Rogue Blitzcrank were two skins that were releases simultaneously for the ADC-grabbing champion, but they weren't available for very long before they were pulled from the store. News that the skins wouldn't be coming back for some time began circulating a few days ago when the projected re-release date was discussed.
Due to a store issue, Lancer Paragon and Lancer Rogue Blitzcrank skins won't be available until 7.24. Sorry for the delay everyone!— Will (@willstarck) November 21, 2017
The nature of the skin-stopping bug hasn't been confirmed, so we don't know exactly why the two skins have been removed outside of knowing that the two were causing problems in the store. However, a recent post on the League boards further explained that Riot Games believes they've isolated the source of the issue and should have a solution soon.
"We've been experiencing an issue with the way the store is handling the Lancer Paragon and Lancer Rogue Blitzcrank skins," a post explained. "We removed them from the store shortly after their release when we found the bug and have been working on a solution since. We think we've found the cause of the bug, but it will take time to implement and so the skins won't be available to purchase in the store until Patch 7.24 at the earliest."
To be clear, this issue only affects the Blitzcrank skins that are in the store. It's been repeated by different Rioters more than once since the skins were temporarily removed, but if you were able to purchase the skins before they were pulled from the store, you'll still be able to use them in-game.
The new skins were a special project where the skin teams looked to create two skins at the same time that were both quite different but also connected. You can read more about Lancer Paragon Blitzcrank and Lancer Rogue Blitzcrank here, and look for their return to the store sometime in Patch 7.24.