I had the same problem. USB transfer/recognition worked on 16.04 OTA 23, then when I upgraded to OTA 25, it did not (https://forums.ubports.com/post/73614). Then, I upgraded to Focal, and it works again. My recommendation, upgrade to Focal.
I had the same problem. USB transfer/recognition worked on 16.04 OTA 23, then when I upgraded to OTA 25, it did not (https://forums.ubports.com/post/73614). Then, I upgraded to Focal, and it works again. My recommendation, upgrade to Focal.