Why does rpm/rpmkeys --import not execute successfully in rpm %post scriptlet in Red Hat Enterprise Linux 8?

Issue

• rpm --import or rpmkeys --import doesn't execute successfully while being a part of rpm package's %post scriplet?

# rpm -q import --scripts
preinstall program: /bin/sh
postinstall scriptlet (using /bin/sh):
rpmkeys -vvv --import /RPM-GPG-KEY-redhat-release
preuninstall program: /bin/sh
postuninstall program: /bin/sh

• This works with Red Hat Enterprise Linux 6 and 7.

[root@rhel6 ~]# rpm -ivh /root/rpmbuild/RPMS/x86_64/import-1-0.x86_64.rpm
Preparing...                ########################################### [100%]
   1:import                 ########################################### [100%]
D: loading keyring from pubkeys in /var/lib/rpm/pubkeys/*.key
D: couldn't find any keys in /var/lib/rpm/pubkeys/*.key
D: loading keyring from rpmdb
D: opening  db environment /var/lib/rpm cdb:mpool:joinenv
D: opening  db index       /var/lib/rpm/Packages rdonly mode=0x0
D: locked   db index       /var/lib/rpm/Packages
D: opening  db index       /var/lib/rpm/Name rdonly mode=0x0
D:  read h#     670 Header sanity check: OK
D: added key gpg-pubkey-fd431d51-4ae0493b to keyring
D:  read h#     671 Header sanity check: OK
D: added key gpg-pubkey-2fa658e0-45700c69 to keyring
D:  read h#     788 Header sanity check: OK
D: added key gpg-pubkey-ab97acbe-586223cc to keyring
D:  read h#     806 Header sanity check: OK
D: added key gpg-pubkey-0608b895-4bd22942 to keyring
D: Using legacy gpg-pubkey(s) from rpmdb
D: closed   db index       /var/lib/rpm/Name
D: closed   db index       /var/lib/rpm/Packages
D: closed   db environment /var/lib/rpm

[root@rhel7 ~]# rpm -ivh /root/rpmbuild/RPMS/x86_64/import-1-0.x86_64.rpm 
Preparing...                          ################################# [100%]
Updating / installing...
   1:import-1-0                       ################################# [100%]
D: loading keyring from pubkeys in /var/lib/rpm/pubkeys/*.key
D: couldn't find any keys in /var/lib/rpm/pubkeys/*.key
D: loading keyring from rpmdb
D: opening  db environment /var/lib/rpm cdb:0x401
D: opening  db index       /var/lib/rpm/Packages 0x400 mode=0x0
D: locked   db index       /var/lib/rpm/Packages
D: opening  db index       /var/lib/rpm/Name 0x400 mode=0x0
D:  read h#     186 Header SHA1 digest: OK (dd737a402556b7653c2bc971f343532046e26384)
D: added key gpg-pubkey-352c64e5-52ae6884 to keyring
D:  read h#     450 Header SHA1 digest: OK (22824a5fcbad49190bcc2dd45d06b4b53aad2447)
D: added key gpg-pubkey-fd431d51-4ae0493b to keyring
D:  read h#    1132 Header SHA1 digest: OK (2355c07f9978587c537d385c0bdd9353214f7032)
D: added key gpg-pubkey-2fa658e0-45700c69 to keyring
D: Using legacy gpg-pubkey(s) from rpmdb
D: closed   db index       /var/lib/rpm/Name
D: closed   db index       /var/lib/rpm/Packages
D: closed   db environment /var/lib/rpm

• The error it throws is as follows. rpm --import couldn't get the Lock.

# rpm -ivh import-1-0.x86_64.rpm 
Preparing...                          ################################# [100%]
Updating / installing...
   1:import-1-0                       ################################# [100%]
ufdio:       1 reads,    17154 total bytes in 0.000011 secs
ufdio:       1 reads,     3211 total bytes in 0.000005 secs
error: can't create transaction lock on /var/lib/rpm/.rpm.lock (Resource temporarily unavailable)
error: /RPM-GPG-KEY-redhat-release: key 1 import failed.
error: can't create transaction lock on /var/lib/rpm/.rpm.lock (Resource temporarily unavailable)
error: /RPM-GPG-KEY-redhat-release: key 2 import failed.
warning: %post(import-1-0.x86_64) scriptlet failed, exit status 2