@kerdosa can you report this to the issues tracker along with a test case showing the problem there. Looks like a bug because it should favor the primary constructor. It might be databind picking the string-only constructor thinking it is a magical constructor that accepts a string JSON and does its own binding. If so, it will be hard to fix in the module. You can test it by adding a second parameter to see if that was the issue. Otherwise report it here:
https://github.com/FasterXML/jackson-module-kotlin/issues