randomdev hangs during initial boot of -current on Raspberry Pi

I hadn't updated my Raspberry Pi 4B running -current for a couple of
months, so I booted the latest snapshot (Jan 27).  It hangs when it
does the "growfs" step, expanding the root partition and fs to fill
the SD card.  When it hangs, it prints this every 10 seconds or so:

    random: randomdev_wait_until_seeded unblock wait

I waited several minutes the first time, and 20 minutes on another trial.
If I hold down the return key on the serial console, the device unblocks
and the boot continues.  This only happens on the initial boot, when the
growfs script runs.  The hang happens on a Raspberry Pi 3B+ as well.
It also happens with the two-week-old snapshot, but not the Nov 25
snapshot.  The program that's running during the hang is awk, doing
a read, according to ^T; the script uses awk to parse output from
mount, glabel, and sysctl.

It sounds like there is no source of entropy at this point, and there
was no cache.  I don't see any changes to the random device since this
was working.  Does anyone have a guess what to look for?  A bisect
would be rather laborious, building a modified SD card each time,
even if just testing kernel changes.  Any other suggestions?

An excerpt from /var/log/messages during this time is appended.

		Mike

Jan 27 10:38:48 generic kernel: umass0 on uhub0
Jan 27 10:38:48 generic kernel: umass0: <ADATA SD600Q, class 0/0, rev 3.00/93.01, addr 2> on usbus0
Jan 27 10:38:48 generic kernel: umass0:  SCSI over Bulk-Only; quirks = 0x8100
Jan 27 10:38:48 generic kernel: umass0:0:0: Attached to scbus0
Jan 27 10:38:48 generic kernel: da0 at umass-sim0 bus 0 scbus0 target 0 lun 0
Jan 27 10:38:48 generic kernel: da0: <ADATA SD600Q 9301> Fixed Direct Access SPC-4 SCSI device
Jan 27 10:38:48 generic kernel: da0: Serial Number 40118905201B
Jan 27 10:38:48 generic kernel: da0: 400.000MB/s transfers
Jan 27 10:38:48 generic kernel: da0: 228936MB (468862128 512 byte sectors)
Jan 27 10:38:48 generic kernel: da0: quirks=0x2<NO_6_BYTE>
Jan 27 10:38:48 generic kernel: random: randomdev_wait_until_seeded unblock wait
Jan 27 10:38:48 generic syslogd: last message repeated 48 times
Jan 27 10:38:48 generic kernel: random: unblocking device.
Jan 27 10:38:48 generic kernel: GEOM_PART: mmcsd0s2 was automatically resized.
Jan 27 10:38:48 generic kernel:   Use `gpart commit mmcsd0s2` to save changes or `gpart undo mmcsd0s2` to revert them.
Jan 27 10:38:48 generic kernel: lo0: link state changed to UP