freebsd stable - Nov 2019 - Boot hangs after exausting uhub2: 7 ports with 7 removable, self powered

Hi!

since 12.1-ALPHA9 FreeBSD wont boot anymore into multiuser. 12.0-ALPHA8 is
ok, but not 12.0-ALPHA9. Same for:

- FreeBSD 11.3_RELEASE, 11_STABLE
- FreeBSD 12.1_RELEASE, 12_STABLE
- FreeBSD 13-HEAD

All on zfs without any ufs slice/partition/disk.
It is the same for amd-64 and arm, arm64 architectures.
Looks like ufs only systems do not have any problems booting.

No hints about any changes to boot processes. ZFS loads, finds zfs:zroot.
After this message some usb related stuff is printed, the last line then is
"usb2: 7 ports with 7 removable, self powered". Module opensolaris.ko
is
build and loads, right together with module zfs.ko. So zfs shall work.
Any idea what is going wrong here?

-- 
Thomas