installkernel: install: /usr/lib/debug/boot/kernel/: No such file or directory *** Error code 71

On CURRENT (FreeBSD 13.0-CURRENT #185 r364767: Tue Aug 25 16:10:50 CEST
2020 amd64), /usr/src at  revision 364907, installkernel fails now due
to an error as shown below. For the record, "options ZFS" ist
statically in the kernel config file.

Also deleting /usr/obj and restarting buildworld and buildkernel from
scratch doesn't solve the problem. The buildworld and buildkernel
mutually finish without error (I do not see any on the console),
installworld also finishes fine, but installkernel not.

/etc/src.conf looks as follows:

[...]
CPUTYPE?=                               native
# World
CFLAGS+=                                -O3
#CFLAGS+=                               -DNDEBUG
# Kernel
COPTFLAGS+=                             -O3
#COPTFLAGS+=                            -DNDEBUG
#CXXFLAGS+=                             -std=c++17
WITH_CLANG_EXTRAS=              YES
WITH_LLDB=                              YES
#WITH_BSD_GREP=                 YES
WITH_OFED_EXTRA=                YES
WITH_NAND=                              YES
#WITH_CTF=                              YES
WITH_SVN=                               YES
WITH_BEARSSL=                   YES
WITH_PIE=                               YES
WITH_SORT_THREADS=              YES
WITH_ZONEINFO_LEAPSECONDS_SUPPORT=      YES
MALLOC_PRODUCTION=              YES
WITHOUT_ASSERT_DEBUG=   YES
WITHOUT_TESTS=                  YES
WITHOUT_PROFILE=                YES
WITHOUT_DEBUG_FILES=    YES
WITHOUT_REPRODUCIBLE_BUILD=     YES

[...]

Debugging facilities are disabled as src.conf indicates.

[...]
install -T release -o root -g wheel -m 555   xz.ko
/boot/kernel/ ===> zfs (install)
install -T release -o root -g wheel -m 555   zfs.ko /boot/kernel/
install -T dbg -o root -g wheel -m 555   zfs.ko.debug
                                      /usr/lib/debug/boot/kernel/ 
install: /usr/lib/debug/boot/kernel/: No such file or directory ***
   Error code 71

Stop.
make[4]: stopped in /usr/src/sys/modules/zfs
*** Error code 1
*** Error code 1