In Alex's Mobs version 1.22.5 and Forge 47.1.28 (and possibly other version combinations) the game will crash whenever the player tries to turn to page 2 in the animal dictionary. The crash report yields the following text:

The game crashed whilst rendering screen
Error: java.lang.NullPointerException: Cannot invoke
"net.minecraft.world.entity.EntityDimensions.m_20388_(float)"
because "this.size" is null

EDIT - This issue is resolved with newer versions of Forge. If encountering this issue, try using an updater version.

Same issue on Forge 47.1.10

I'm having the same issue.

This happens because of rendering CombJelly.
Perhaps this is due to the use of Optifine

Reference: #1707

dupe #1796