Hi Dan,

sorry, forgot to mention: Sequoia ist Windows only, my system: Windows 10, Intel i7, 64 bit.

Did some tests, VST3 / 64bit and VST2 / 64 bit, with Pink Noise stereo, left channel only, right channel only

VST3 sums both inputs to mono, output channels L/R carry the same signal

VST2 works as expected, no summing.

Hope this helps, 

Gerhard