Mob regains concentration and continues casting while stunned.
 

Should mobs still be able to regain concentration and continue casting while stunned?

https://imgur.com/ljMJOMy.jpg

Looks like it's flagged unstunnable. You can still 'stun' mobs flagged like that but they don't actually stun. E.g. giants and such. And the stun only gives a chance at interrupt, like a bash, it's not guaranteed.