I jave the same problem . I am on ipad 1 5.1.1 mirroring on i can watch other sources but kodi has display greyed out so i can not switch to anything else
AppleTV4/iPhone/iPod/iPad: HowTo find debug logs and everything else which the devs like so much: click here
HowTo setup NFS for Kodi: NFS(wiki)
HowTo configure avahi (zeroconf): Avahi_Zeroconf(wiki)
READ THE IOS FAQ!: iOS FAQ(wiki)