Having used Lollopop on my M8, and my S6 - this makes no sense (no pun intended) - The following is from the Droid Life (p)review:
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Lollipop Notifications

On LG devices that run Lollipop, the company seems to have broken expandable notifications. This same issue was documented in our G Flex 2 review. When you have a notification, such as Gmail or Twitter, they are usually expandable for viewing. On LG devices, however, they are not. On the lock screen, they work just fine. You can expand, compact, and swipe away. Just as it should be. But when your phone is unlocked and you pull down your notification shade, you cannot interact with the notifications. You either swipe away or click on them. Since this is not the way Lollipop was made to work, it’s a big time annoyance coming from any phone that works properly. Hopefully LG addresses this issue in a future update.