Hello, I have the same issue described here https://github.com/qooob/authentic-theme/issues/731 and I did upgrade to Authentic Theme 18.47. But for some reason still can't use the editor, all the opened files are blank with exactly 1 line, but at least now you get an window. Cleared cache, restarted the browser, cleared caches, restarted Webmin, restarted the whole server - no effect whatsoever. I am scared to even think what happens if I type something and save... Or I don't type anything and just hit save.
Can you guys check with Ilia, it seems he can't reproduce the problem?