All you need to do is to:
- Select all the thumbnails.
- In the Fill panel, select "Original Size" as the fitting option.
- Make sure that you are using "upload to the FTP host" in Muse, instead of exporting and uploading manually. You can find this option under the *Files > Upload to FTP host*.
- In the "upload to the FTP host" options, do **not** check "Only modified files", but instead select "All files".
- Preview the page in your computer, before uploading and if the issue is not showing up on preview but on uploaded version, then some files are missing in your FTP, then use a FTP client, remove all the files for that Muse project from your FTP, then upload it again, using "upload to the FTP host".