Hi and welcome to Arturia forums.
I use Studio One 3. If things has'nt changed, then the midi channel settings is'nt availble for VST3 plugins. Studio One give priority to the VST3 plugins. So if you have VST3 plugins installed, Studio One is set to use VST3 plugins, then i guess nothing has changed, and that's your issue.
You need to use the VST2 versions of Arturia plugins to do what you wan't.
I can't tell if it's an issue that's about Arturia or Presonus. I know Studio One 3 does'nt have the same issue with all VST3 plugins, and i assume it's the same in Studio One 5. The other plugins you mention that work might be VST2 plugins or VST3 plugins that's different from Arturias. I know Kontakt is VST2 only.
I think this midi channel selection issue for VST3 plugins in Studio One is an annoying issue, and i wonder, why Arturia and Presonus have'nt found a solution yet. I use the VST2 versions because of this, but would like to use VST3 plugins.