During an attempted GWToolset upload last year I encountered a problem when trying to upload some larger images 730Mb. The problem I encounter is that I get a HTTP timeout reply already at the second stage of the upload process.
@Dan-nl has also tried debugging this one for a while and concluded that there seems to be something wrong with the http-request that uses curl to discover the headers of the item which for some reason times out even though it's only requesting headers and not the file.
For testing the relevant xml is {F26865}, the mapping is at [[ commons.wikimedia.beta.wmflabs.org/wiki/GWToolset:Metadata Mappings/Lokal Profil/KB-maps.json | GWToolset:Metadata Mappings/Lokal Profil/KB-maps.json ]] and an example image for further testing can be found at https://data.kb.se/datasets/2014/06/kartor/2882568_53_Skargardskriget_hagelsta.tif