Hi,
I have tried everything im/possible to update to 1903 but was not succesful. Finaly I decided to reinstall the whole system on new hard drive. It went smoothly.
I am really dissapointed that it had to go this way... as it seems, this is not a problem of few unlucky souls.
Hope others were luckier and did not have to reinstall...
just as unlucky if I have to lose all my programs every time there is an update I'm buying an apple