Hi,
@larry
The issue you encountered was related to the compatibility problem with the atcom tool. I have upgraded the tool to the latest version, which is now compatible with the current version of Raspberry Pi OS, resolving the communication problem with the module. The disconnection of the USB connection is due to the Sixfab CORE services restarting your module for cellular connection purposes. This is not an issue, an expected behavior.
@s-shige
Do you have Sixfab CORE installed on your device as well?