Problems with Images in spreadsheet header/footer
Currently neither Libreoffice (in xlsx) up to v6.4.1 nor Onlyoffice (v5.4) manages images in header/footer in a spreadsheet document.
This means that it is not possible to preview them in GoFAST (as a reminder, GoFAST Enterprise v3.7 renders XLSX with LibreOffice, DOCX and PPTX with OnlyOffice)
A enhancement request has been filed for Onlyoffice here : https://github.com/ONLYOFFICE/DocumentServer/issues/801
For LibreOffice a bug is currently opened here : https://bugs.documentfoundation.org/show_bug.cgi?id=122107