Unable to create new alert checker

Hi,

Sorry to be of a pain, but I had to migrate Observium from Ubuntu 16.04 to 18.04. This has been successful and I have been able to copy over the sql database as well as the rrd folder.

All seemed to be ok until I tried to create a new alert checker. I am able to fill in all the information required, but clicking on 'Add Checker' does not do anything. The 'Clear Rules' button does work though.

I have tried looking into the apache logs as well as mysql logs, but nothing seems to be reporting.

Other alert checkers are still there and I am able to edit and save the changes. It just seems that I am not able to create new ones.

I am on build 20.1.10233, if you need more information, I am happy to supply this.