The Bug
The Illager Beast constantly hesitates to move when a pillager is riding it, causing it to become much less of a threat. It only exhibits this behavior in pursuit mode.
How to Reproduce
Trigger a village raid and wait for an illager beast to spawn with a rider and place a villager at least 12 blocks away from it.
Linked issues
Comments 3
Actually it is technically a duplicate of MC-139304 (which also contains more detail)
Do MC-137579 or MC-138976 describe your issue?