I found that the audio FFT input gain control in audio preferences does not apply on startup until you open the preferences window. I am currently using Arena 5.0.1.
To reproduce:
1. Save a composition with an external audio FFT input on a parameter.
2. Close and then restart Arena so it restarts the program then reopens the comp.
3. Expand the effect/parameter so you can see the FFT audio input level
4. Open the preferences window and note the level change as the gain control is applied.
FFT Input Gain Bug
Re: FFT Input Gain Bug
Confirmed and ticket made, thanks for letting us know!