Here is what we did to solve this issue.Add the following dispatcher rule to /etc/httpd/conf.dispatcher.d/filters/publish-filter.any (adjust to your path):/0261 { /type "allow" /method "POST" /path "/content/forms/af/[A-Za-z0-9-]*/[A-Za-z0-9-]*/jcr:content/guideContainer*" /extension '(jsp)'}  # all...

I am also getting this same error with AEM 6.5.9 with AEM Forms:[AF] [AEM-AF-901-004]: Encountered an internal error while submitting the formSubmitting the form on Author is OK, but submitting on Publisher is returning (in Chrome's Console):POST [domain]/content/forms/af/[form-folder]/[form-name]/j...