Firstly - I know that Adobe recommends uploading sites to an FTP server. That is not the way my server works. I have been "export(ing) to html" for the past two years and my site has worked just fine.
PHEW! Now that that's done...
Since the update, my export doesn't work. I've tried new files. I've tried emptying my web server and starting over. Nothing is working. Has anyone encountered this before?
Many apologies to find you in this trouble.
Please try to change the path/ location of your HTML export to a new one and see if that works.
However, If it still doesn't work would you mind sharing your .muse file with us so that we can investigate and try fixing it?
For sharing the file you can follow the steps explained here - https://forums.adobe.com/docs/DOC-8652 and send the link to me in a private message.
For doing a private message hover the mouse on my picture and click "message".
Can you please a screenshot of the credentials box? I mean the one which says site URL and location.