📄How to Fix the Error - Post Splitting Multi Venue "Cannot Duplicate key in object 'dbo.KeyListItem' The Duplicate key value is etc"
In short: Delete the Keylists from Keymaps, Delete the Keylist, re-create Keylist with Product Profile, and add Keylist button back to Keymap.
Run Smartcontroller

You will see Duplicate Key Errors
If you see errors such as these: The numbers in the error are: Keylist ID (such as 11790 in this example) Followed by Product Number, and size. The important thing here is the Keyllist ID
In Backoffice, Open Product Profiles

Open Product Keymaps

Click View/Edit Keylists

Find the Keylist ID/s that appear in the Smartcontroller errors)
Click Delete Keylist.

This will then show us which Keymap/s we need to remove the Keylist from as part of the solution).

Open the Keymap/s indicated in the previous step.

Locate the Keylist/s in question. (Be sure to copy and Override Text names to add back in) Take a screenshot if need be).

Right click and Clear Key Function
Save the Keymap but leave it open as we need to add the Keylist button/s

Go back to the Keymap List Tab

Click View/Edit Keylists

And Delete the Keylist ID in Question. (It will allow us now it has been removed from the Keymap).

Click on the Product Profiles Tab

Click Re-Create Keylists

Go back to the Keymap you removed the Keylist from

Add the Keylist button back on. Right Click

Set as Keylist

Select the Keylist you deleted which will now be re-create

Correct the button Colour Override name if required

Save. Repeat for all Keylists in the Smartcontroller errors.

Close Smartcontroller

Upon restarting Smartcontroller errors will be cleared.