Map disappearing from BaseCamp?

My new Zumo 396 LMT-S updated its map and software by wifi. When I plugged the GPS in to the PC it uploaded the map from the GPS to BC, but it disappeared from BC when I unplugged the GPS. I found Garmin Express and installed the map ( North America 2019.20) to the pc. This seemed to work for a day or so, then map disappeared from BC. I used Express to reinstall it, but now when I unplug the GPS from the PC, it disappears from BC?

Can I only use BC with the GPS plugged in?