iOS 11 and missing apps

Apple has required all new iOS apps and app updates submitted to the iOS App Store to support 64-bit since June of 2015. Starting with iOS 11, apps that haven't. complied will either not appear or not launch in iOS 11. The only way to proactively check is to go to Settings -> General -> About -> Applications and review the list of apps shown there. If you have apps there that you currently use, you may wish to make plans to work around them this Fall. Note this doesn't apply to iPad 2s: they can't run iOS 11 so don't have this issue.