You were correct. It turned out for some reason the Dongle was appearing to only work with AC18. It had worked in the past with AC19 so what happened to it I don't know.
We upgraded it and it seems to fine now.
AC versions 3.41 to 25 (UKI Full 5005).
Using AC25 5005 UKI FULL
Mac OSX 10.15.7 (19G2021) Mac Pro-2013 32gbRam AMD FirePro D500 3072 MB graphics