Timeouts during initial Mode Sense commands

[Denver Hull]

Hello,

I have several different microcontroller boards that are supposed to 
appear as storage devices when plugged in.  They work fine on Linux 
systems, but on FreeBSD 11.3 and 12.1 they don't show up at all. Here's 
what dmesg shows for one of them:

ugen1.3: <Adafruit Industries LLC PyPortal> at usbus1
umodem0 on uhub1
umodem0: <CircuitPython CDC control> on usbus1
umodem0: data interface 1, has no CM over data, has no break
umass3 on uhub1
umass3: <CircuitPython Mass Storage> on usbus1
umass3:  SCSI over Bulk-Only; quirks = 0x0000
umass3:5:3: Attached to scbus5
uaudio0 on uhub1
uaudio0: <CircuitPython Audio> on usbus1
uaudio0: No playback.
uaudio0: No recording.
uaudio0: MIDI sequencer.
uaudio0: No HID volume keys found.
ums2 on uhub1
ums2: <CircuitPython HID> on usbus1
ums2: 16 buttons and [XYZ] coordinates ID=2
(da3:umass-sim3:3:0:0): got CAM status 0x44
(da3:umass-sim3:3:0:0): fatal error, failed to attach to device
g_access(944): provider da3 has error 6 set
g_access(944): provider da3 has error 6 set
g_access(944): provider da3 has error 6 set
g_access(944): provider da3 has error 6 set
g_access(944): provider da3 has error 6 set

There's a definite delay after the last ums message.  I used camcontrol 
debug in single user mode on a bare 12.1 system to get a little more 
information about what was happening.  It looks like the initial Inquiry 
and Test Unit Ready commands succeed, but the next Mode Sense command 
times out, as well as all subsequent commands. There are several seconds 
of inactivity between retries, and there's no sense data, so I'm 
assuming that indicates timeout.

At this point I'm not sure how best to proceed to get these devices to 
work, so any help will be appreciated.

Regards,

Denver