Which custom fields are we talking here?

@Isram Any chance you could give us a screenshot of someone who is having the issue?  Is it one PU profile, one PU user? Or is it a global issue?

Are the PUs limited by branches or groups? Wondering if the field is not visible to the same branches that the PU has access to…

This might be because of the Advanced Setting for additional field visibility.  You might also need to put the power users into a branch that has been assigned visibility to those additional fields. 

I did a quick post with instructions on how to fix this, it might also work for your power users as well?

Am thinking you need to grant visibility via the branches under User Management

on the slide out panel, choose the fields you want the PU to access

Hope this helps