Presently, this is still an issue. Somehow, this shows up as a duplicate post. I tried to lock this thread so there would only be one, but clicking the lock pad doesn't seem to accomplish that.

Some tome types no longer allow you to “use on pet” to boost its stats. The tome seems to behave as if it’s an egg, which only allows you to boost up to a certain tier.

I am playing on a Windows computer, and the pet I’m trying to boost is tier nine. Using these has never been a problem before, and my entire battle coliseum strategy revolves around the use of tomes to boost optimally.

Once I ran into this issue, further testing shows that both tomes of ice and wind are affected. These cannot be used on my pet to stat boost at this time. The other types of tome (darkness, death, earth, fire, life, light, magma, and water) appear to function normally, at least with my tier nine pet.

Please take a look at this feature. I am eager to return to my usual play/battle training style!