Starting with the Tumbleweed snapshot installed on March, 29th I got back an
old error

systemd-cryptsetup: Device root is still in use.
systemd-cryptsetup: Failed to deactivate: Device or resource busy

which shows up in the journal after switching root.
I am not sure, but I believe that the reason for this is

systemd[1]: plymouth-start.service: Unit process 394 (plymouthd) remains
running after unit stopped.
systemd[1]: Dispatch Password Requests to Console Directory Watch was skipped
because of a failed condition check (ConditionPathExists=!/run/plymouth/pid).

which shows up in the journal just before the "in use" message.
So plymouth didn't stop and the encrypted filesystem couldn't be unmounted.

Before the last two snapshots the message looked like this:

systemd[1]: Condition check resulted in Dispatch Password Requests to Console
Directory Watch being skipped.