Hey gang, this may be a known issue but I figured I'd mention it anyway. I've updated Hitfilm Pro 2017 a few times without using it much lately, and then last night when I went to dig into a really involved project I noticed that a bunch of my effects were missing, including the mocha plugin. I had just updated to the latest patch, if it's relevant. Anyhoo, I re-downloaded the main installer from my Account page and ran it, selecting the Repair option, and everything came back. Not sure what happened, but hey.
Interesting thing, when I tried loading a project I knew had a mocha effect in it, (before running Repair) Hitfilm told me "this project uses a plugin that Hitfilm can't find."