This was discovered when Studio One 6.6.1 was released. v6.6.1 contains the latest v3.7.9 VST SDK, which might be the reason for causing this.
This has been confirmed in the S1 user forums, and one user is reporting this issue also in Cubase (they didn't say which version).
Both Q3 and L2 work in every other surround and Atmos format, but not specifically in 5.1.2. It used to work before the S1 v6.6.1 update.
I have my Atmos rig configured for 5.1.2, and to get these plugs to work right now, I use 7.1 for the time being.
Note I haven't tried VST2, as I no longer have VST2s on my system and have that specially engine disabled in S1 (found generally S1 performs quicker and a lot more stable not using any VST2s).
This was discovered when Studio One 6.6.1 was released. v6.6.1 contains the latest v3.7.9 VST SDK, which might be the reason for causing this.
This has been confirmed in the S1 user forums, and one user is reporting this issue also in Cubase (they didn't say which version).
Both Q3 and L2 work in every other surround and Atmos format, but not specifically in 5.1.2. It used to work before the S1 v6.6.1 update.
I have my Atmos rig configured for 5.1.2, and to get these plugs to work right now, I use 7.1 for the time being.
Note I haven't tried VST2, as I no longer have VST2s on my system and have that specially engine disabled in S1 (found generally S1 performs quicker and a lot more stable not using any VST2s).