This seems to be a partial regression of MCPE-12443, but I've created a new ticket as I think the base issue is different.
Angered pigmen do not run fast enough; the player is able to outpace them by walking.
According to the wiki:
When aggravated, their speed will significantly increase to faster than the player's walking speed.
I think changing the speed multiplier from 1 to 1.5 in the vanilla behaviour file for this mob would fix this:
"minecraft:behavior.melee_attack": {
"priority": 3,
"speed_multiplier": 1.5,
"track_target": false
},
Fixed a couple minor versions back. Zombie pigman speed is now multiplied by 1.5 when they are chasing a target.