Raising the limit of Treedropdown field

Questions
1

Silverstripe Version: 4.7.2

On a large site when users are trying to link to a page, a root page with more than 250 children renders without any children.

How to increase that limit?

I tried:

SilverStripe\ORM\Hierarchy\Hierarchy:
  node_threshold_leaf: 300

In my app.yml - no effect after a dev/build?flush…

I set it down to 50 to remove a different parent and that didn’t go either.

What is the correct setting or way to set this limit?