Windows 10 Update may disable your administrator account
Updating Windows 10 1803 to the current version 1809 may disable the default administrator account. This always happens if both this account and a user account with administrator rights are existing at the same time.
It is therefore advisable to make sure that you have access to this other user account before you start the update. Otherwise it may happen that you lose your administrator rights if you are using the default administrator account. After the update, the default administrator account can be reactivated if necessary. Normally this account is disabled anyway. It is only active if you don't create a new admin account during the setup process of your windows system or if activated it after the setup process manually.
Microsoft is currently working on a solution to the problem. The company expects to have a new version of Windows ready by the end of January.
In general, we do not recommend to use the default administrator account, as this account is intended to be used if your actual account is compromised.