Hey @Luca_Ceriani
If you have not changed the job type it will keep on using same plugin it copied. So you might have changed the plugin in the Repo the Worker cache needs to updated.
To do that the easiest way to test is to re-load plugin between the tasks. It is not recommended for rendering because it takes more time to render (loading and unloading plugin on every task ). So for any job you are trying to test> right click it> Modify Job Properties> General> Re-load plugin between tasks. Then retry, if it still fails, check if you have got a copy of plugin in the [repo]/custom/plugins/3dsMax/, if you have this plugin will used rather than the one in the default folder. So you will need to make changes to that plugin. If it still fails attach the copy of 3dsmax.py you have got in [repo]/custom/plugins/3dsMax/ or if you do not have it in custom get from [repo]/plugins/3dsMax/