Thank you again for your help. My problem was finally fixed by doing this. I do realize that my ssd may be failing, but that was never the problem. Somehow the 1903 update kept trying to find C:\windows\system32\migration. This is where the whole problem was, so I followed these instructions and deleted that folder. Voila..system updated. Now all is well. For anyone with this same error, please try this.
The installation failed in the SAFE-OS phase with an error during MIGRATE_DATA operation.”
SetupDiag reports fatal migration plug-in failure.
Plug-in Name = %windir%\system32\migration\SxsMigPlugin.dll
Migration Operation = IPostApply->PostApply
Plug-in Error: 0x00000002
(0x0000002 means 'file not found')
I got it working by deleting:
c:\windows\system32\migration
You might need to fiddle with owner rights and permissons. But get the whole thing with subdirs and files gone.