yum/dnf fails with 'Failed to obtain the transaction lock. Error: Could not run transaction'

Issue

• yum/dnf transactions fail with:

Running transaction check
Transaction check succeeded.
Running transaction test
Transaction test succeeded.
Running transaction
Failed to obtain the transaction lock (logged in as: root).
The downloaded packages were saved in cache until the next successful transaction.
You can remove cached packages by executing 'dnf clean packages'.
Error: Could not run transaction.

OR

Running transaction
RPM: error: selabel_open: (/etc/selinux/minimum/contexts/files/file_contexts) No such file or directory
RPM: error: Plugin selinux: hook tsm_pre failed
The downloaded packages were saved in cache until the next successful transaction.
You can remove cached packages by executing 'dnf clean packages'.
Error: Could not run transaction.