Offline Bounce Weirdness

[blastula]

Getting differing results between offline and online bounce in the following condition: (and I understand that my routing is stupid!)

I've got 2 bass tracks (DI and Amp)
I chose bus 19 as their output destinations.
And I chose bus 19 + 20 as the input source for the Stereo Buss
The Buss is panned L100% and R100%.
The bass in the online bounce sounds centered perfect.
The bass in the offline bounce sounds panned far left.

I know, effed up routing. but why the difference in bounce results?

update:
i flipped the phase on the DI track, the result was a fuller sounding bass, but the ofline bounce was still sounding hard left.

and then:
I used a mono buss (input source buss 19) instead of the stereo buss.
kept the phase flipped. This time, both bounces had the bass centered, but the Offlne bounce Bass sounds weaker (lower volume and thinners sounding) than the Online bounce.

In all cases the ONLINE bounce matched what I was hearing through the Stereo Master track. In all cases the OFFLINE bounce didn't.

(This was all done immediately after I had trashed preferences)

Any thoughts on why?

[Darryl Ramm]

Some systems details might help? You running native? Ultimate on HDX?

[blastula]

Ultimate 2019.10.0
HDX1
Mac Pro Mid 2012 (pre trashcan)
OS 10.14.6
Ram: 40 GB
2 x 3.46 GHz 6 Core Intel Xeon

after doing some forensic work: i found that the reason the 1st bass buss was stereo is because i accidentally chose a mono to stereo plug....in the screen shot you can see a de-activated 1176. that's the one.

STILL, the question remains: why does the Offline bounce behave so differently than the Online bounce?

[Darryl Ramm]

Well when you have HDX the first suspicion is always because you are switching between AAX-DSP for real time and AAX-native for offline bounce. Any differences are easily caused by a plugin bug...

You can try real time bounce with all native plugins.

You can keep disabling plugins and see if you can find something that makes the difference go away.

Or maybe it's something else... so do these tests quickly.

Are you doing anything fancy like sidechain compression?

[blastula]

no sidechain compression. no hardware inserts. i guess nothing fancy.