PT12 Play Start/Stop Lag

[QTM]

Greetings, gents. If I may, I could really use your help.
I'm having a couple of issues. I'll split them up as different threads to keep it clean.

We are a post facility, and we just upgraded from PT10/OSX MtnLion/BlackMagic to PT12.8.1/OSX Sierra/AJA LHi.
Running:
MacPro Towers 5,1 2.66 12cores, 48gb ram.
HDs are all Samsung SSD 850 Pro.
Capturing video with AJA ControlPanel,
Translating video with MPEG Streamclip.
We've tried every iteration of DNxHD.

Very simply, push play= lag. Push stop= lag. Total varies, but is around 1.5 to 2 seconds. Every single time.

Longest lags come from alternating the playback from opposite ends of even just a 30 second spot.

I can minimize it to PT10 levels if I Disable Video Hardware, and/or turn off Delay Compensation.

True, we work at an extremely fast pace, but I'm not seeing a lot of complaints about this since PT11 (which we skipped).

No, Count In is not enabled.
No difference when changing "Play Start Latency"
Changed Synchronization values, no change.
Changing Video I/O does nothing.
Have tried looping in Sync HD with house ref, including feeding reference to AJA Kona LHi through a breakout cable, nada.
Switched over to BM, same issue.
PT 12.8.2 didn't solve it. In fact, it just added a few more turds.
Even obsessed over the AJA ControlPanel settings with the editors/machine room monkeys.

This is super frustrating and diving us nuts. May even roll back to PT10.
There are other issues, like, not being able to see System Preferences while PT is open, and lagging automation during playback if you click or change any automation, but I'll start new threads for that.

Thanks so much, fellas! I really appreciate those of you who take the time!

Thanks