Dear Maintainer,

   * What led up to the situation?

I had another machine that gave kernel panic while upgrading from Stretch to
Buster. Use of Graphical install was also a problem during re-install due to
destroyed system. (I reported this issue in another report.) Thus, I chose to
upgrade an identical machine from level 1 (Debain Repair in GRUB2 boot menu).

   * What exactly did you do (or not do) that was effective (or
     ineffective)?

The scrolling log in the command line display showed repeated
connect/disconnect loops for USB devices (of many kinds). This applied also to
USB mice and keyboards connected via KVM.

For what it was worth, I used a local cache of the DVDs on the machine's hard
drive.

Unplugged all USB, plugged in single USB keyboard only, and directly, not via
KVM.

   * What was the outcome of this action?

Upgraded fine with just the keyboard directly plugged into USB.

   * What outcome did you expect instead?

Correct handling of USB, without issues.