When running a Nintex Installer, or running the Upgrade-NFService command in the SharePoint Management Shell, you receive the following message:

Upgrade-NFService : Invalid object name 'DatabaseVersion'

To resolve this issue, you have two options:

Recreate the Nintex Forms database.
-Navigate to Central Administration > Nintex Forms Management (later changed to Nintex Administration) > Manage Database (later changed to Database Management) > Edit the Display Name of the database > Click 'Ok'. Your Nintex Forms are now mapped to a newly created database with the DatabaseVersion table.

Note: You may find that the Nintex Forms Database that has been in place is empty. This database is only used for Nintex Live Forms, Nintex Mobile Forms, and other external facing forms. If you do not leverage any external facing Nintex Forms, the above method will have no impact. If you do have data, please consider the next option.

Recreate the DatabaseVersion table.
-In SQL Server Management Studio, navigate to your Nintex Forms Database (called NintexFormsDB by default) > Right-click your Nintex Forms Database and select 'New Query'.
-Recreate the table with the following query:

CREATE TABLE [dbo].[DatabaseVersion] ([Version] [nvarchar](max) NOT NULL,[LastUpdated] [datetime] NOT NULL) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]

Once the table is created, add an object to the table:

INSERT INTO [dbo].[DatabaseVersion] (Version, LastUpdated)VALUES ('1.0.0.0', 1/1/2019)

Once the above two queries have been executed, please run the Upgrade-NFService command. Once the command is executed, you will see the values in the DatabaseVersion table resemble the following:

Version	  LastUpdated4.1.0.0	  2019-09-18 22:49:17.227

Upgrade-NFService : Invalid object name 'DatabaseVersion'

This message suggests that the DatabaseVersion table in the NintexForms database in your environment is missing. There is currently no known root cause of this table disappearing, but tends only to happen while updating Nintex Forms in On-Premises SharePoint environments.