Hello,
Please make sure that you are using the latest version of Dokan-lite (v2.8.2). If you are using latest and still getting the error then there might be a script loading problem.
The following section provides instructions for determining if an issue you are experiencing with is caused by a theme or plugin conflict.
1. Theme Test
=> Switch to the default WordPress theme as we know that the default WordPress theme is coded properly. Now try to edit product and see if the issue is still there. Take note if you see a difference in behavior after you have switched the theme. Switch back to the theme you were using.
2. Plugin Test
If the theme didn’t have anything to do with the issue then move on to the plugins section. There are many WordPress plugins out there and not all of them are coded nicely so let’s see if you have a plugin installed that is not playing nice.
=> Try to deactivate the plugins excepts Dokan then check again.
If you have any other questions, just let me know and I will be happy to help you.