I've had this issue in the past and it was apparently caused by USB microphones just randomly not being identified with OBS. Fixing it is usually as simple as unplugging the microphone and then plugging it back in. If you are using push to talk for audio recording with OBS, make sure that you rebind your TFAR keys to accommodate your OBS since it only allows 2 keybindings for PTT. I reversed the long range radio and alternate channel keybinds to solve this issue since I do not carry a long range and I typically am not a driver in a vehicle. Hopefully this helps, let me know if it doesn't.