Here is what I would do if I were in your situation.
Make sure you have either a full backup or an image taken of your system drive.
Then uninstall Cakewalk by Bandlab and then uninstall Bandlab Assistant.
Reboot your PC
Make sure you have version 3.09 of the installer - I say this because you can't tell if you have simply by looking at the filename of the installer. All versions have the same filename. Version 3.09 has an exact file length of 45,587,528 bytes
The latest version is available from here:
https://www.bandlab.com/download/assistant/windows Reinstall Bandlab Assistant. Log on with Bandlab assistant (I am assuming you're using the same email address that you used for cakewalk before November 2017)
Then via a logged on Bandlab assistant, install Cakewalk by Bandlab - this should bring you to Build 31 of Cakewalk by Bandlab.
Note: Once Cakewalk by Bandlab is installed and running, you do not have to have Bandlab Assistant running. I usually exit it suing the cog and exit. Clicking on the X at the top right leaves Bandlab Assistant resident. I only run Bandlab Assistant to check for and install any updates for Cakewalk by Bandlab.
If this does not get you out of Demo mode than you might want to head over here to log a support ticket.
https://help.bandlab.com/hc/en-us/requests/new Hope that helps.