Do you try to reduce its size by forming pdf file instead of word file? It worked for me after I contacted the online support from Elsevier submission system, they replied me and asked me to reduce the file size.

Already PDF. I would NEVER post a MS Word file. It's large, but that is not the problem. I have tracked the issue to two PDF files which were subsets of the single consolidated file I created. These are error-free PDFs (afaik) which open fine in Adobe Acrobat Reader without complaints. But if uploaded to Research Gate the system abandons them without diagnostics or error messages. Simply hangs for a long time and abandons. Same effect with SMALL files on their own.