Sidechain Bug - Studio One v3.5.4

I've been experiencing a problem where I'm not seeing some plugins to be sidechained in my list of sends. The plugin that I'm am trying to sidechain does indeed have the capability of doing so. Sometimes the issue is fixed if I close and reopen Studio One, other times it is not.

I'm currently attempting to sidechain to Waves F6 Dynamic EQ plugin, but this is not the only plugin I've experienced this problem with.

Are there any additional steps I'd need to take or consider in order to successfully sidechain chaels?