Q: Extensions crashing the Photo App

Have you installed the most recent updates for Affinity Photos and the MacPhun applications?  And the update to MacOS X 10.11.2?

I had a similar problem on my MacBook Pro late 2011.  The extensions worked well on the iMac, but not the MacBook Pro. It helped to reinstall Photos by booting into Recovery and reinstalling the system on top of the current system.  See:  OS X: About OS X Recovery

It is suspicious, that all extensions are having issues, not just one. That's why I think a system update might not have installed correctly, like it happened on my MacBook Pro.

It could be a problem of your Photos Library as well. You could test this by creating a small Photos library for testing.  Just launch Photos while holding down the options key and select to create a new library. Import a photo for testing, then try to use an extension.  Does it work in your new test library?

Good Luck!

It is good to know, that this worked in your case.

In some cases extensions are missing from the System Preferences panel, because they need reindexing. The procedure is explained in this support document:  If Share options or Markup is missing after upgrading to OS X Yosemite or El Capitan - Apple Support