[cctalk] serial comm help Linux

Well, everything is a fight! The project I'm working on is to get a VMS MicroVAX system working at VCFMW.  The plan was to have serial comm on a Linux laptop connected to the MicroVAX.  I have the serial comm working on a Dell desktop machine, so I just plugged the same USB serial cable into the laptop, and NO COMM!  I plugged back into the desktop, and serial data works fine!  I'm totally mystified!  The desktop is running an OLD Debian kernel (7.11), the laptop is running a late Ubuntu (24.04.4). I have no idea why the laptop doesn't communicate.  I have tried minicom, picocom and cutecom, same result on all of them. Thanks for any help you can suggest. Jon