You have Visibility Rules enabled for a field on your form, but the field is not shown or hidden as expected based on the values in the other fields.
If you have enabled visibility rules for Field B but the field is not showing/hiding as expected when the correct value is chosen in Field A, one possibility could be the with the setup with the selected operator in the rule. When using visibility rules for Field B, the "is" operator will use and reference the displayed values of Field A, but "contains" will use the stored values.
For example, let's say you have a visibility rule that should display the a particular field when 'Marketo Lead Management' is selected for the "Product Interest" field. The displayed value for the field (the one shown to the customer) may be "Marketo Leads Management" but the stored value for the field (the value written to the lead record) is "MLM".
If you set up the visibility rule as "Product Interest is Marketo Leads Management", the rule will look at the Display Value and see a match. However, "Product Interest contains Marketo Leads Management" will look at the Stored Value, which is "MLM." It will not see the match, and the field will not be displayed.