Solution: Home Assistant OS, Windows 10, VirtualBox and deCONZ problems
I, like others have struggled with ongoing USB passthrough stability with the following set-up:
Core Machine: i7 NUC, 8GB
Host OS: Windows 10
Guest: Home Assistant OS 2021.3.2
Issue was constant dropping (daily or more) of Conbee 2 stick that is feeding deCONZ natively installed through HA. Errors included:
cdc_acm 2-4:1.1: acm_start_wb usb_submit_urb(write bulk) failed: -19
cdc_acm 2-4:1.1: failed to set dtr/rts
Finally came to the conclusion that the issue is primarily the instability of VirtualBox handling of the USB passthrough of the Conbee 2. I believe this is the culprit, though an associated kernel issue could be as well.
Decided to install and run deCONZ natively on the Windows 10 machine, avoiding having to pass the Conbee 2 through the VM. Unfortunately, had to reassign all devices in HA but was well worth it to achieve stability. Most recent Win10 deCONZ ver. 2.10.2 works well with HA Phoscon/deCONZ and has been smooth sailing ever since.