Checkbox clears when checked with autofill enabled

2) This does not help. As mentioned, the form is set to autofill. I want
the customers to check items when they are completed over a span of time
(the checklist will NOT be completed all at once). In testing, I noticed
previously checked items were uncheck when I would reload the page

Thank you for the clarification. I finally understand now that you are using the Autofill feature. Apologies if I have overlooked it in the first place.

However, I couldn't reproduce the problem on your form using different browsers. Reloading the page does not clear the selected options on the checkbox field.

Screencast:

Please take note that when the form is submitted, it will automatically clear the form. Furthermore, this feature requires browser cookies. If your browser cookie is disabled, this feature will not work. We suggest turning if on. Thanks!

The issue occurs with the previously checked item is changed. Take the
hyperlink for instance, if a checkbox is changed in anyway the previously
checked item becomes unchecked.
...

I tested your form and was unable to replicate your issue, I can see that the autofill feature is working as it should.

Could you please try again? 

which browser are you using? 

Please, check if the browser cookie is enabled, do let us know if it works now.