I gave that a go as well, still the same.
On another MacBook, I've removed all of the old CC 2018 apps and have installed CC 2019 manually rather than re-imaging the device and have DeployStudio carry out that process.
I can sign in and the apps do work fine now, so something must go slightly wrong during the imaging process.
In the meantime, I'll just have to install it on each device manually.
Thanks for your help though!