Hi there!
I’ve got the same issue as @jakelong here, but on latest vanilla engine from launcher (4.21) with latest FMOD (1.10.10) on C++ project. It happens if you’re starting project with debug attached via Visual Studio on this project when another UE4 project (without FMOD) is already open. I know it kinda specific, but it doesn’t happen with any other UE4 plugin. So, please take a look at this.