Error installing SQL Server Database Engine Services Instance Features - The User Log directory in the registry is not valid

We have a SQL Server: >Microsoft SQL Server 2017 (RTM-CU14-GDR) (KB4494352) - 14.0.3103.1 (X64) Mar 22 2019 22:33:11 Enterprise Edition (64-bit) on Windows Server 2016 Datacenter 10.0 (Build 14393: ) (Hypervisor) Tried to install "Cumulative Update Package 18 for SQL Server 2017 - KB4527377" https://www.microsoft.com/en-us/download/details.aspx?id=56128 Setup was doing something for 15 min, installing and updating files, stopping / starting services, it looked like its going to succeed, but in the end it showed this: > Action required: > >Use the following information to resolve the error, and then try the setup process again. > >Feature failure reason: > >An error occurred during the setup process of the feature. > >Error details: > >Error installing SQL Server Database Engine Services Instance Features The User Log directory in the registry is not valid. Verify DefaultLog key under the instance hive points to a valid directory. Error code: 0x851A0044 Visit https://go.microsoft.com/fwlink?LinkId=20476&ProdName=Microsoft+SQL+Server&EvtSrc=setup.rll&EvtID=50000&ProdVer=14.0.3257.3&EvtType=0xD8FB5EBA%400x97A656BB%401306%4068&EvtType=0xD8FB5EBA%400x97A656BB%401306%4068 to get help on troubleshooting. What's preventing CU18 from installing ?