Various errors can occur while creating a smartform, which prevent that a process definition is deployable. Indeed, if the smartform is erroneous, either an error occurs already at deployment and fails, or the smartform is not visible in the client.
Sources of errors
the syntax of the smartform is incorrect. This can be checked with the following validator. This should display no errors anymore so the syntax can be excluded as a source of error.
The same ID was used for multiple elements. Thus, the alocation of the process variable is no longer correct and the right fields can not be filled with the appropriate information.
if the custom.js is not loaded, errors are located in the syntax and prevent the smooth functioning.