If there’s some problem with Windows Updates (or it can be due to other reasons too), the CBS log file can grow faster than it’s rotated and after a while it can’t be rotated.
The log files are under C:\Windows\Logs\CBS.
Both CBS.log and any uncompressed log files can be hold by the Trusted Installer service preventing deletion. So, to clean up safely:
net stop TrustedInstaller del C:\Windows\Logs\CBS\CBS*.log net start TrustedInstaller