/usr/local/lib/systemd/system is a location where systemd sources system units,
as stated in systemd.unit(5).

On a default install of openSUSE Tumbleweed, with a root filesystem of type
btrfs, and with snapshots, /usr/local is mounted as a subvolume to avoid it
being modified in case of an OS rollback.

This combination causes systemd units under /usr/local/lib/systemd/system to
not work properly. Service and timer units stored there are found, and can be
enabled, but they don't actually run as expected on reboot.

If ext4 is used as root filesystem, it works as expected.

Tested on Tumbleweed 20230728.