Microsoft published information on a new known issue that may cause connectivity issues for some Storage Area Network (SAN) devices via the Internet Small Computer System Interface (iSCSI) Microsoft does not yet provide mitigation measures or workarounds for this issue. Users can still resolve their iSCSI-based SAN connectivity issues by uninstalling the cumulative update which causes them in the first place. Microsoft also resolved a number of other issues impacting Windows 10 version 1903 that were behind several, now removed, update blocks.
Source: https://www.bleepingcomputer.com/news/microsoft/windows-10-may-2019-cumulative-updates-break-iscsi-san-connectivity/