It happened to me after using umount -a; followed by mount -a;

some directories became read-only; remounting it with rw solved; but I guess I did not cover it all.

... manually creating the file folder structure for each active service with

mdkir /sys/fs/cgroup/systemd/[slice]/service 

followed by: ...

chmod o+rx /sys/fs/cgroup/systemd/ -R systemclt daemon-reload systemctl daemon-reexec 

solved the issue without restart (had to avoid it as we have services running) Important notice: used chmod -R

It happened to me after using umount -a, followed by mount -a.

some directories became read-only; remounting it with rw solved; but I guess I did not cover it all.

... manually creating the file folder structure for each active service with

mkdir /sys/fs/cgroup/systemd/[slice]/service 

followed by: ...

chmod o+rx /sys/fs/cgroup/systemd/ -R systemctl daemon-reload systemctl daemon-reexec 

solved the issue without restart (had to avoid it as we have services running) Important notice: used chmod -R