I have this beautiful new Publish box that I created, and it worked only when Piklist Demos was active. This happen on my dev environment, and in messing around, I got it to work by changing the name of the file while Piklist Demos were active, It then worked when I deactivated the demos.

When I pushed the changes up to staging I have the same issue again and changing the name doesn’t resolve it (likely it’s not the thing that resolved it before, it just happened to coincide with whatever else I did that actually solved it.)

WP Multisite 4.8.1
Piklist 9.9.12

So, in staging, the custom Publish box works consistently while Piklist Demos are active, and goes back to the default publish box when Piklist Demos are deactivated.

Here’s my header block:

/*
Title: Publish
Extend: submitdiv
Extend Method: replace
Context: side
Priority: core
Post Type: pro-cards
*/