Yes, FRIDAY the 13TH!
htc m8 face unlock disappeared
No, it didn’t. I assume we’re talking about m8 with the new lollipop update. Things changes in new version. And in Lollipop: that is totally different. I’ve covered that HERE before.
how to remove the partion cache from htc one m8
Well, you don’t remove it. You simply wipe it clean. I’ve written about that HERE
smart lock not showing htc
In order to use that, you HAVE to enable a lockscreen with a credential (password/pin/pattern). AND make sure that the trust agent for smart lock is enabled. I’ve written about it HERE