[Plugin: Post Thumbnail Editor] "Post Thumbnail Editor" Link Doesn't Appear

I have used Post Thumbnail Editor without issue for the past 6 months or so on version 2.0.0. Today I tried to upgrade to the latest version 2.1.0, and when I did, the “Post Thumbnail Editor” link didn’t appear where it usually does (or anywhere that I can find).

I usually access it via the media display pane, as shown in this screen cap:

http://grab.by/mMOk

Since upgrading, the “Post Thumbnail Editor” link is simply gone. I downgraded back to 2.0.0 (after trying 2.0.1. and having the same issue) and now the link appears again. I tried clearing my cache, logging in and out of WordPress, using a different browser, no avail.