Yep, they both can’t (shouldn’t) talk to the USB stick at the same time.
I’m not sure the best way to do that. Probably the easiest is to just disable the ZHA component (in the YAML or whatever) while you’re using Bellows in the terminal.
In the ZHA Configuration panel, check the LQI (Link Quality Index) and RSSI (Received Signal Strength Indicator) values. LQI less than 255 indicates packet loss. RSSI should ideally be something like -75 dB or better (e.g. -75 is better than -85).