Apple Mach-O Linker ID error

I am working on an audio plugin and have suddenly come across this Apple Mach-O Linker ID error when trying to compile VST3. When I look it to it further it says: " Undefined Symbols for architecture x86_64: " and then lists an AudioBuffer I declared in my AudioProcessor class.

Since my last successful compile I have added a new class which inherits from juce::Thread and am trying to get another thread running to do some of the more expensive audio processing that’s required. However I am pretty new to threading. I’m not sure if this is being caused by that or something else entirely. I have never run into this error before and have mixed reports about it online some saying that it’s a “ghost error” that just goes away sometime however I have closed and reopened Xcode via projucer several times.

Any know what this might be refer? The other threads on the topic don’t address it with VST 3.

I can’t recall if I have compiled since I updated my Mac, but that could also be part of the issue I am currently running

I am running Mojave 10.14.6

Edit: I just tested a Demo and they still compile and work so seems the problem must be within my code. Has anyone expereicend this error before? Ideas on what it could be related too?