When using a Managed Metadata term value within a text field, such as an email body, or Log To History action, the term displays as 'Value | TermIdGUID'
Example: 'Nintex Engineer | b664989e-0ac2-4d49-9a89-d6f7bf092fe1'
This is expected behavior when converting a Managed Metadata term to a string. You can use the Regular Expression action with the following configuration to strip out the GUID: