UPDATE: I can now get the slowdown to happen by launching the VM running Windows 10 and launching a twitch stream or youtube video on the host. If I'm not doing anything in the windowed VM everything's cool (even when it is visible). If I start clicking the desktop in the Windowed VM like crazy frames start dropping on the stream in the host OS. Sound does not skip a beat. This is the same issue I experience constantly while in coherence. This never happened in v.12. I'm about to try and downgrade to v.12 to confirm.
UPDATE 2: Downgraded to v.12 issue persisted. Unplugged second monitor and went into coherence and had no slowdown what so ever. Plugged thunderbolt display into different thunderbolt port and still no slowdown now. I'm at a loss. Upgraded back to v.13 and still no slowdown. This could just be an issue with my macbook or a recent update from Apple. Possibly the different thunderbolt ports on the side of my macbook have different speeds? I'll repost if the issue crops back up again.
Last edited: Nov 25, 2017