Don't use ascii characters with parameter descriptions.

IN CRM 2016/365 when you include speech marks in the description box for a parameter, and then save and close the process, when you open it up again, the parameter will have completely disappeared -  no warning message or validation error or anything.

Looks like someone from the dev. team forgot to XML-encode the parameter description. As a result, the saving custom action will wipe clean your entire parameter list when the descriptions contains one of the following: "&'<>.

Don’t be fooled by the presence of the parameters after you press the Save button – they are good as gone at this stage.