Using Drupal 8.2.7, we are not seeing this issue in 8.2.6
We have a content type that includes a required image field. Alt field is enabled and required, as well as the Title field. When we attempt to add new content of this type, we will select an image for upload from our local drive, and after we choose we notice that no preview or alternative text field appears. After attempting to save the content, we will be prompted for the alt text and we do see a thumbnail preview. Right after selecting the file for upload, our console is showing an AJAX error:
Uncaught
Drupal.AjaxError
message: "↵An AJAX HTTP error occurred.↵HTTP Result Code: 200↵Debugging information follows.↵Path: /node/add/product?element_parents=field_product_image/widget/0&ajax_form=1↵StatusText: OK↵ResponseText: "name: "AjaxError"
__proto__: Error
at http://<our_site>/sites/default/files/js/js_KozRDxBErHUfJMA7BgEUnamnTZc671T13mIssv8-wXY.js:2890:32
at http://<our_site>/sites/default/files/js/js_KozRDxBErHUfJMA7BgEUnamnTZc671T13mIssv8-wXY.js:4053:3
Drupal.Ajax.error @ js_KozRDxBErHUfJMA7BgEUnamnTZc671T13mIssv8-wXY.js:3674
complete @ js_KozRDxBErHUfJMA7BgEUnamnTZc671T13mIssv8-wXY.js:3219
t.complete @ js_ZGVf7yyqX4XiBdN49CivMYwoCyt-AJMaBxLWwhfPoxk.js:565
i @ js_KozRDxBErHUfJMA7BgEUnamnTZc671T13mIssv8-wXY.js:2
fireWith @ js_KozRDxBErHUfJMA7BgEUnamnTZc671T13mIssv8-wXY.js:2
z @ js_KozRDxBErHUfJMA7BgEUnamnTZc671T13mIssv8-wXY.js:4
(anonymous) @ js_KozRDxBErHUfJMA7BgEUnamnTZc671T13mIssv8-wXY.js:4
We have tried changing the thumbnail sizes in the form-display settings for this content type to no avail.
The two pictures attached show before and after attempting to save, with form validation and thumbnail appearing after.