You will receive the following error when running a license check.
Updating cPanel license...Done. Update Failed!
A License check appears to already be running.
This may be due to the Systemd bug reported here. If so, you will see that inodes are exhausted on /run. You can check this with the command below. It will show 100% if this bug is affecting you.
# df -i /run/
Filesystem Inodes IUsed IFree IUse% Mounted on
tmpfs 458752 458752 0 100% /run
If this shows 100%, you can verify further with the command below which will show an inode usage similar to the above.
# du --inodes --max-depth=0 /run/systemd/system/
You can reboot the server to clear the systemd session files.