Email already in Use Error - Changing Employees to Contractors - DO NOT DELETE WITHOUT TELLING ME WHY

My first post of this problem was deleted without any sort of message or notice why. I would appreciate some communication before this action is immediately taken.

I am needing to switch over three employees in my QB to contractors. I have already terminated all the required employees, modified their names and adjusted the email addresses on file, using the exact same naming and email conventions for all three, as per all the other forum posts I was able to find covering this topic.

Ex. John Smith, has been changed to J. Smith. Email profile has been swapped from [email address removed] to [email address removed]

In attempting to proceed to set them up as contractors, I am receiving the below error:

'This email is already in use for an existing user. Please provide a different email for this contractor to complete their profile.'

Strangely enough, I only received the above error for 2 of the former employees. The invite link was successfully sent to the 3rd, even though I have used the exact same process and naming conventions.

I need a resolution to this that does not require setting up new email addresses for these individuals. That is not an option.