It seems that the problem comes from getting a 404 Not Found when retrieving /static/studio//js/vendor/tinymce/js/tinymce/themes/modern/theme.js, which in fact does not exist.
Which does exist is js/tinymce/themes/silver/theme.js, note that the path refers to a silver theme instead of modern. According to this github issue, modern theme was replaced with silver in version 5.
We’re at Palm version, deployed with tutor. We’ve been searching how to update the reference to use the TinyMCE silver theme, but with no luck until now. We even tried a temporary fix copying the silver theme into a modern theme folder in the CMS container : cp -r ./common/static/js/vendor/tinymce/js/tinymce/themes/silver/ ./common/static/js/vendor/tinymce/js/tinymce/themes/modern/, but we still got 404.
It seems to me that the bug does not stem from the edx-sga xblock, because this xblock does not contain any reference to the tinymce editor. Instead, I’d bet that the bug comes from edx-platform/common/static/js/vendor/tinymce/js/tinymce/jquery.tinymce.min.js:
Yes, I’ve come to the same conclusions regarding that call at jquery.tinymce.min.js (I’ve even tried a hot fix changing “modern” to “silver” there with no luck).
Although there is no reference to tinymce in edx-sga xblock, other problem types such as ORA self-assessment work just great (loading the correct theme):