Karax’s “Architect of War” prestige talent states that chrono boost can be used on defensive structures to increase their rate of attack. However, this only works if the Karax player is the one to use chrono boost.
If Karax’s ally is also Protoss, and that ally uses chrono boost on one of Karax’s photon cannons, it will not increase the rate of attack of that cannon.
imgur .com/jO0U4DU.png
If it is only intended for Karax’s own chrono boost to have this effect, then the bug is that other commanders can chrono boost towers at all.