Boris FX has not qualified Media 100 Suite for macOS Sierra (version 10.12). Media 100 Suite v2.1.7 should be considered "beta" software for this new OS. For those who are willing to try v2.1.7 with Sierra, please report feedback on the Media 100 Facebook Group or at Creative COW. When testing beta software, we strongly recommend setting up a test system, and not installing the software on a system you are counting on production.