Tends to be out landed and hit a good bit which leaves him open to losing rounds.
Max and Volk out landed him pretty easily, but the constant pressure and power eventually got to them. Fighters like Ilia don't last long at the top, they get hit too much and are willing to trade blow for blow. Every elite fighter has been able to outland him, and every competent striker has been able to outland him or keep the margin very close (aside from Emmett).
A fighter with better measurables than Ilia who utilizes good activity, movement, and kicks will give him a lot of trouble. Then combine that with a good wrestling threat and his pressure game will be halted.
IIRC Max Holloway only defended his belt 3 times, much like Ilia he was this young unstoppable force of nature. Then when he fought someone who didn't fold early, and was able to outland him over 5 rounds he lost and could never beat that guy (Volk).
I think the same will happen to Ilia, I would be shocked if he could go undefeated in his next 4-5 fights.