Upon plugging in a USB flash drive to the computer, plasmashell (such as the
panel, launcher, and krunner) freezes and become completely unresponsive for
several minutes. During this time I can use programs in open windows and kwin
continues working, but I cannot interact with plasma itself. After a few
minutes, the new disk becomes available and plasmashell usually starts working
again.

I am not sure whether the root cause is in plasmashell, udisks, or somewhere in
between, but of course the shell is not expected to freeze while waiting on a
background job.

While the shell is frozen, it logs this output:

kf.solid.backends.udisks2: Error getting props:
"org.freedesktop.DBus.Error.NoReply" "Did not receive a reply. Possible causes
include: the remote application did not send a reply, the message bus security
policy blocked the reply, the reply timeout expired, or the network connection
was broken." for "/org/freedesktop/UDisks2/block_devices/sdi"
file:///usr/share/plasma/plasmoids/org.kde.plasma.devicenotifier/contents/ui/DeviceItem.qml:36:5:
Unable to assign [undefined] to bool