Hi Gareth,
I think that Mendix supports the connection to MSSQL 2016 and 2017 as can be found on the following page: https://docs.mendix.com/refguide/system-requirements#8-databases.
Not sure if the version that you have is supported.
Hope this helps.
Cheers,
Jeffrey
I was running into the same issue and I was able to fix it as follows:
In MS SQL Server Manager I changed the compatibility level to 2017 under Properties → Options
After that the application was able to run locally.