This issue has been driving me crazy but at least I now know the cause. I made another thread about this, but was thinking it was some kind of network issue only I was experiencing because it was almost like very micro lag where buttons just did nothing.
I use variations of this macro for like 99% of my buttons so I was constantly having spells failing.
#showtooltip
/targetenemy [noharm][dead]
/stopmacro [channeling:Mind Flay/Mind Flay: Insanity/Void Torrent/Penance/Dark Reprimand/Ultimate Penitence/Divine Hymn]
/cast [spec:3] Mind Flay
/cast [spec:2] Smite
/cast [spec:1] Smite
I guess I just gotta git gud until they fix it.
Blizzard, please fix this ASAP. Casters that actually have to cast and channel a lot (priest) feel infinitely better with these type of macros.