I've just spent the last week trying to track down an issue I've been having when playing live in Synchron (VEP6 and VST3 single instance) in Cubase 10 on macOS 10.14.3. I was getting lots of red CPU overload warnings in Synchron and most notes being cut short or not sounding at all. Weirdly, this only happened with I played live, but not if I played back a pre-recorded MIDI track. It happened with all of the Synchron libraries including the pianos.
Initially I thought the problem was with my SSD. After buying new cables, and even using a Faraday bag and tinfoil, I found out the culprit was the high buffer setting in Cubase. I had it set to 2048; when I reduced it to 1024 the problem vanished. I'm glad I solved it because I was about to buy a new SSD I was that fed up and desperate.
I'm just posting this here in case any one else has this issue. I have no idea why this caused Synchron to throw a wobbly, but it seems it does not like the high buffer setting.
Cheers!