Hi,
you do not have to set all fields to "Visible in Front End" in order make the summary page button working.
What do you mean, when you say "I have no javascript validation anywhere in my form." Does this mean, that javascript validation is not working (you expect javascript error messages but they do not show up), or that you do not have any fields in your form of which you think that they require any sort of validation?
Actually almost any form has some fields that needs some sort of validation (i.e. field of type email, number, date... are validated for proper format, required fields are validated for the existence of an input, file upload fields are validated for proper file format and size and so on.).
On a multi page form the validation of the user inputs is check separately for each page. If the other "next" and "back" buttons on the previous pages work and only the summary page button does not I can think of only one reason for your problem, that there is an invalid user input but the javascript error message is not displayed properly. I have experienced this problem some times myself, mostly in combination with templates, that do not provide the Joomla! standard conform Bootstrap 2.3.2 css but use some sort of adapted Bootstrap 3 css or if the template on your website is a Bootstrap 3 template but you have not selected a Bootstrap 3 layout for your form in the form configuration.
I think, the first step to solve your problem would be to check, if it is caused by this conditions.
It is a bit tricky to check, if this is the reason for your problem. But basically if a field is validated with javascript and the user input is not valid, the validator sets a class attribute "error" for this field. If you check the HTML of your website, using the browser console, (open console, go to form, make user inputs, until you have clicked the "Summary page" button) and there is a field with class="error" in the active fieldsest, then, but you do not see an error message, this would confirm my theory.
The next step would then be, to check, if changing the form layout, helps (you sometimes need to refresh the page twice, maybe clear Joomla! and Browser cache after this change), before it really shows up.
If you cannot figure a solution, I would need a link to the form, to look into this.
Regards,
Aicha