Using the Facebook messenger app, I came across an issue where when I sent a message on my HTC One M8 running stock android 5.0.1 with sense 6 unlocked, it would sometimes freeze for around 10 seconds, locking up both the app and most of the functionality of my phone.
Since I've had this issue and have been able to replicate it after using HTC's tool to reinstall my OS and only the messenger app, I figure other people will as well.
Sorry for the keywords, trying to make this google-able on the chance other people have this issue with their HTC One M8 on lollipop unlocked or developer edition phone using the Facebook messenger app.
The issue seems to come from the in-app sounds. When my phone is on silent or vibrate, I can send messages without the hang or lag, but as soon as I turn the ringtone volume up passed muted, it starts to go really slow again.
My solution to this is to go into the fb messenger app settings, and uncheck the box that says "in-app sounds".
I have sent multiple reports of the bug to Facebook, so hopefully it'll be patched soon enough.