USB comms - Arduino, Termite works, Putty, Raspberry Pi doesn't work

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I am working with an ESP32-CAM with a ESP32-CAM-MB board and have run into a bizarre problem with serial communication. I was able to burn the Edge Impulse (https://www.edgeimpulse.com/) firmware onto the ESP32 using a Raspberry Pi and their shell script, which invokes esptool. The firmware appears to write OK. Using esptool to query the chip id seems to work - it returns an id that changes when I swap ESP32 modules. However the Edge Impulse daemon cannot see the ESP32.

This is where it gets really weird. Using screen, I can't see anything on the USB port. I take the ESP32 and cable over to a different computer and I can see the firmware transmitting messages over USB if I use the Arduino serial monitor or the Termite serial program. However if I use Putty I see nothing. No messages, no gobbledygook, nothing at all, even if I reset the ESP32. I have checked (and re-checked) baud, port settings, flow control, local echo, CR/LF. I've tried resetting the ESP32 while watching output from Putty. I've also tried a different PC and gotten the same results.

Burned firmware with esptool on Raspberry Pi - works
Queried chip_id with esptool on Raspberry Pi - works

(above shows that serial port, cable and ESP32 are good, I believe)

View USB output with screen and minicom on Raspberry Pi - nothing
View USB output with Arduino serial monitor and Termite from Windows 10 PC - works
View USB output with Putty from Windows 10 PC - nothing

I'd like to understand what is going on here. Can anyone offer an explanation?
thx