I'm having issues with the enemy castbar disappearing as well. Seems very random, happens in combat and out of combat. Bar just... goes away.
I have updated to the latest version. I have also deleted the files from Saved Variables to "reset it" to stock settings. I use this addon "Without Externals," not sure if that effects anything. All the dependent libraries are installed and activated.
I have this problem too.
I make my wow "nacked" I leave only Archud2. Same problem. If i use some special attack, enemy castbar is disappearing. I hope somebody can help/fix this.
p.s.: Sorry for my bad english