Thanks, yeah I should have mentioned what version I’m on. I am indeed using this “7.0.13” version already, specifically on commit 95b49f668b with the update to VST 3.7.11 and 9.1.6 changes. This hasn’t made any difference though --I’ve seen the same behavior in previous 7.X versions I’ve used.
Do you see the same behavior in REAPER, or not have this issue?
EDIT: I should note the channel order in the SurroundPlugin demo is also flipped in REAPER when using 7.1 or 7.1.4 surround if you edit the isBusesLayoutSupported to support these layouts. REAPER doesn’t play very nicely with the demo by default, since it gives it more or less free reign when setting the bus layouts.
As far as I’ve been able to tell, the flip is only occurring for layouts that have Lss/Rss and Lrs/Rrs specifically. I’m not sure if it’s REAPER incorrectly flipping the channels, or something in the VST3 SpeakerArrangement conversion like I reported here: Possible bug in VST3 channel order mapping.