Why can't I Holy War?

[Pompey MCCXCVII]

I'm playing as Doge of Venice. I swore fealty to Byz early on, and converted to Iconoclasm. I was initially able to holy war, but when Byz Emp renounced Iconoclasm, I stayed Iconoclast and I'm no longer able to holy war. In fact I was in the middle of a holy war when Byz Emp made the decision. I do border some Slavics in Croatia and Serbia, and Crown Authority is at medium, so I can't figure out what the problem is.

Not using mods, Active DLCs are:
Charlemagne
Legacy of Rome
Sons of Abraham
The Republic
Way of Life

 

[Whizzer]

To holy war, you must be of the same religion as your (top) liege.