Systems compiled from source freeze right before transferring control to init

[Thomas Schweikle]

Hi!

I am facing a quite bad problem: I've compiled
- FreeBSD 11.2, 11.3, 12.0, 12.1-BETA-2, 12.1-BETA-3, 13-CURRENT from
sources. All went ok so far. But booting these leads to systems freezes
right before kernel transfers control to init. Last lines are about found
uhub-devices. Sometimes "random: unblocking device" is additionally printed.
But thats it. Systems wont come up, booting into multiuser. Booting to
singleuser does not help either. Booting an fresh install from freebsd.org
provided ISOs has the very same problem. Going back to sources before
2019-09-01 makes everything work again except 12.1-BETA-3. This stops then
with zfs error 45, because zfs on disk uses features not available with zfs
from these older sources.
This freeze occurs with a variety of different virtualization software as
on real hardware:

VM:
- VMware Workstation 15.0.1, 15.5.0, 15.x.pre
- VirtualBox 6.0.10, 6.0.12
- KVM with Ubuntu 19.10, openSUSE tumbleweed
- MS-Hyperv Windows 2016 Server, 2019 Server (Beta)
- bhyve on FreeBSD 12 before 2019-10
- Intel Core i3, i5, i7, 20GiByte RAM each, 4TB, SATA-SSD

Within /usr/src/UPDATING i could not find anything not set or enabled as
expected. Any idea where to look further?

-- 
Thomas