Shop workaround
Hello,
Went to buy Cass today (I've seen Kalista and am more of a fan of supporting her than playing her, so I didn't buy her) and realized exactly how bad the shop lag is. I couldn't buy her through the store, but when checking my champions out in my profile and selecting her, I could purchase her there with no delay and it worked on the first try. As this is the only example I have, I can't guarantee this will work for those having trouble with the shop, but it's worth a shot!
Hope it help! Spiritriser