"Insert links" feature not working

I am working on editing a post and adding links to other content on my site. When I highlight the text I want to link and then click the “insert links” button, nothing happens. The link buttons are not grayed out so they appear active, but nothing I do brings up the add links feature. I was not having this problem with the last version of WordPress, so maybe it is an update issue? I have tried editing this post on Firefox and Chrome, and I have used two different computers.

I would appreciate any help or advice. Let me know if you need more information. Thanks!