Users that are copleting my survey on mobile are receiving the error 'mimimum NaN' although they have completed all the required fields. 

It works ok for other usesrs. 

Is there any way to fix this error? 

Thanks 

UPDATE: 

im using version 3.8.3 

there doesnt seem to be a section in the questions that refer to minimum answers - under 'basic info' tab each one is Mandatory, and I've set up no conditional rules for the survey. 

Thank