What is wrong if I can skip all the questions and complete the survey. I require all the questions to be answered before completing survey. Also on mobile devices I am only showing forward next button no ability to go backwards.
What types of questions are you seeing this with?
Grid Questions for example, may require one row to receive an answer if you have not specified a minimum rows answered requirement.
Also, do you have the ‘forward only’ setting enabled on the survey? I would expect this to be enabled when seeing what you have described in the mobile view:
I hope this helps you troubleshoot!