I am unsure if this also happened before the latest round of updates which brought the build up to 18362.239 as my investigations have all been done today on the latest build. I have 4 machines at my house today. 2 have 3rd party anti-virus on them 2 have Defender as resident anti-virus on them. The 2 which have Defender as av both get 'cannot repair corrupt files' when running a system file check. Defender is mentioned in their CBS logs. All machines have 1903 build 18362.239 on them. Could anyone who has 1903 and runs Defender check if a SFC completes without an error?