Debian 10 Buster. Virtual com ports disappear, don't respwn

Generic older Dell desktop
Debian 10, Buster

Almost daily I have to reboot the machine I maintain RealPort software on, and use for collecting data from remote scientific instruments that I use Digi One SP devices to interface with. This isn’t a new issue for me, but the frequency is. I reboot the machine 3-5 times per week. The frequency increased when I installed an instrument in an area with poor cell coverage (I use cellular broadband modems for Internet). I’m right on the edge of coverage so the Digi’s presence fades in-and-out. But this issue doesn’t only affect that device and virtual port, but a bunch of others with stable Internet connections as well. It’s as if the one unstable connection has infected all.

  1. Why are the virtual com ports disappearing?

  2. Why don’t they spawn/respawn when the Digi is on-line?

  3. Is there a command I can run to avoid rebooting the machine?