#datelist

Bert, I don't see how is it possible for this module to cause the issues you are describing.

Please provide me with some additional data on the tests you are performing:

• What is the Drupal version you are using in your test (major and minor version, like 11.0.9)?
• Do you know what is the theme being used in the form instance you are mentioning?
• Is the problem you are raising associated with a node form, or is it another entity?
• Is this entity in a context of being added or edited?
• Is this field limited to one instance, or multiple instances?

Now, some questions associated with your particular testcase description:

• You mention date-list element in this sentence: "After installing date-list element (...)". The module's name is partial_dateist. Just to be on the safe side: are you sure you installed partial_dateist?
• When you say "add element to form", do you mean you created a date or datetime field?
• What do you mean by "Select Date part and order"? Did you open the settings form associated with the date field on this page admin/structure/types/manage/[date-type]/form-display? In case you did, did you save the form display at the end of the page?
• What date parts did you decide to hide? Was it the day only, leaving Year and Month unchecked?
• When you mention "Set Title Display and Description to invisible", do you mean that you moved both the Title and Description fields to the Disabled section of the form display?
• Aren't you adding two different date fields in your form?
• Can you provide me with a screen capture of your form configuration on this page (admin/structure/types/manage/[date-type]/form-display)?
• If you simply uninstall the module, does the problem persist or go away entirely?

Please, provide me this additional information so I can get more perspective on the issue you are documenting here. As I said before,

Thank you!