Hero not appearing in level 50 Mayhem Missions

[Zephyr Star]

I couldn't find any topics mentioning this, though admittedly my powers of searching is not impressive.

After my character robs a bank, I see the text pop up that a hero is on the way. They never show up. I've tried:

Waiting by the vault. Only Longbow and then the Kheldian Cops show up.
Waiting downstairs. The same.
Clearing cops around the bank.
Clearing any side missions.
Exiting and reentering.
Clearing entire map.

All I want is to get the badges from mayhems, including Hero Slayer. I know there's other ways to obtain that particular badge but I was hoping to get them all together.

Is there anything I'm missing to get this to work or am I just not a good enough villain and the hero has better things to do?