Since Muse has been discontinued and support is no longer availible — has the 'upload to FTP host' been disabled as well. It may be a coincidence but I have two live Muse websites and both will not upload with this feature.
I get the message 'Failed to retreive MD5 fingerprint from server'.
Has anyone else had any trouble uploading their websites via this method since the 1st April?
Upload to FTP hasn´t been disabled except PCs had this issue in the recent past.
On my Mac everything works as intended and expected.
If using a PC, unfortunately the last and only possibility might be to upload via File Zilla or any similar ftp-app.
Contact your host. Ask if they've changed anything on their end.
Also refer to this help article from A2 hosting.