Microsoft has just stopped distributing Windows 10 Insider Preview 18875 (20H1 development branch) for Windows 10 V1903 Insiders. A bug probably causes issues with the update installation.
Windows 10 Insider Preview Build 18875 (from the 20H1 development branch) was released on April 10/11, 2019 for Windows Insiders in the Fast Ring and Skip Ahead Ring. Now there is a supplement in the Windows Blog from April 16, 2019:
UPDATE 4/16: A huge thank you to all the Windows Insiders who reported and up-voted feedback on receiving 0xca00a000 and/or 0x80242016 errors when attempting to download and install Build 18875. Your feedback has been immensely helpful in the investigation of the issue. We have determined that there is an issue with the Build 18362.53 (KB4495666) Cumulative Update that was released early last week which has caused updates to Build 18875 to fail. The issue only impacts 19H1 to 20H1 updates and occurs due to a migration failure as the OS attempts to update to the new build. To resolve this issue, we are creating a new Cumulative Update that will need to be applied on top of Build 18362.53 first before Insiders will be able to update to the latest 20H1 builds. As we work on this new Cumulative Update, we have stopped offering Build 18875 to Insiders on Build 18362.53 and holding off flighting a new 20H1 build until we can deliver the fix to unblock Insiders. Our goal is for this to happen by the end of this week. We’ll share additional updates as available.