Freeform 3.9.0 introduced some changes to the included sample Formatting Templates. These changes likely only affect a small number of sites. If any of your forms are 1) using the default example formatting templates, 2) not using AJAX, and 3) you are translating the main success and error banner messages, you may be affected. If all 3 of those conditions apply, please update your language string to be 'Sorry, there was an error submitting the form. Please try again.' and place it inside the 'site.php' translation file (instead of 'freeform.php'). If your site only has 1 language, you can also consider switching to use the new Validation tab approach where the messages can be set inside the form builder per form.