I used usb debug tracing to get a couple more event log errors when reproducing the disconnect: USB-USBXHCI error 34 and USB-USBHUB3 error 123.
According to my tech support assistant Bing Chat:
The event ID 34 means that the USB 3.0 driver (USBXHCI.sys) failed to start a device on a port. The completion code 19 means that there was a transaction error on the port. This can happen if the device or the cable is defective, or if there is interference or noise on the bus.
And about error 123 Bing says:
Based on the information, it looks like you have encountered a port change request failure on port 3 of your USB 3.0 hub. This means that the hub driver failed to reset the port after a device was connected or disconnected. This can cause the device to become unusable or unrecognized by the system.
I’ve sometimes thought there was an EMI interference possibility given how weird the problem is (and the fact that there were EMI shielding problems in early framework models). Once again, according to my IT guy Bing Chat:
Noise on the bus can cause error 34 because it interferes with the communication between the USB controller and the device on the port. Noise can be generated by various sources, such as coil whine, dirty USB power, damaged USB port, or incompatible USB cable. Noise can affect the signal integrity and cause errors or data loss during the USB transactions. A transaction error means that the USB controller detected an error in the data packet or did not receive an expected response from the device. This can prevent the device from starting or functioning properly on the port.
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