idImageManager::ImageFromFile
    *_name = 0x05c72e20 "fms/_missionshots/previewshot_gatehouse_2014-01-29_19.24"
idMaterial::ParseStage
    src.buffer = 0x05c8f2e0 "material fms/_missionshots/previewshot_gatehouse_2014-01-29_19.24 // IMPLICITLY GENERATED\n{\n\t{\n\tblend blend\n\tcolored\n\tmap \"fms/_missionshots/previewshot_gatehouse_2014-01-29_19.24\"\n\tclamp\n\t}\n}\n"
idMaterial::ParseStage (diff function same name)
    src.buffer = 0x05c8f2e0 "material fms/_missionshots/previewshot_gatehouse_2014-01-29_19.24 // IMPLICITLY GENERATED\n{\n\t{\n\tblend blend\n\tcolored\n\tmap \"fms/_missionshots/previewshot_gatehouse_2014-01-29_19.24\"\n\tclamp\n\t}\n}\n"
idMaterial::Parse
    *text = 0x05c8f2e0 "material fms/_missionshots/previewshot_gatehouse_2014-01-29_19.24 // IMPLICITLY GENERATED\n{\n\t{\n\tblend blend\n\tcolored\n\tmap \"fms/_missionshots/previewshot_gatehouse_2014-01-29_19.24\"\n\tclamp\n\t}\n}\n"
idDeclLocal::ParseLocal
    This function has no parameters
    idMaterial::Parse called with declText as parameter
    declText = 0x05c8f2e0 "material fms/_missionshots/previewshot_gatehouse_2014-01-29_19.24 // IMPLICITLY GENERATED\n{\n\t{\n\tblend blend\n\tcolored\n\tmap \"fms/_missionshots/previewshot_gatehouse_2014-01-29_19.24\"\n\tclamp\n\t}\n}\n"
    declText is from the function GetText()
idDeclLocal::GetText
    void idDeclLocal::GetText( char *text ) const {
        HuffmanDecompressText( text, textLength, (byte *)textSource, compressedLength );

}
    textSource is a class member of idDeclLocal

So it's obviously reading the compressed file and getting the incorrect file name for that
So I searched for "IMPLICITLY GENERATED" in the solution and found

bool idMaterial::SetDefaultText( void ) {
    // if there exists an image with the same name
    //if ( 1 ) { //fileSystem->ReadFile( GetName(), NULL ) != -1 ) {
    char generated[2048];
    idStr::snPrintf( generated, sizeof( generated ),
                    "material %s // IMPLICITLY GENERATED\n"
                    "{\n"
                    "\t"    "{\n"
                    "\t"    "blend blend\n"
                    "\t"    "colored\n"
                    "\t"    "map \"%s\"\n"
                    "\t"    "clamp\n"
                    "\t"    "}\n"
                    "}\n", GetName(), GetName() );
    SetText( generated );

    return true;
}

So it is probably returning the incorrect name from GetName()

(Virtual functions are a pain to debug)

GetName is from idDecl::GetName
GetName( void ) const { return base->GetName(); }
base is class idDeclBase* but again that's an abstract class
The abstract class is actually idDeclLocal:

const char *idDeclLocal::GetName( void ) const {
    return name.c_str();
}

?name.c_str()
0x758b5653 "\aÑ\xe"

So that doesn't give us anything, let's go into the idStr::snPrintf function

This is putting the wrong file paths in
So something to do with setting the name of the idDeclLocal?

Did a search of the solution with various breakpoints, name is being set in line 1703 of DeclManager.cpp


decl->name = canonicalName; where canonicalName is the incorrect filename

It is being called in the function idDeclManagerLocal::FindTypeWithoutParsing where name is 0x18f75b60 "fms/_missionshots/previewshot_gatehouse_2014-01-29_19.24.32859"
Called from *idDeclManagerLocal::FindType where name is again incorrect
Called from *idDeclManagerLocal::FindMaterial where name is incorrect
Called from idWinBackground::Set where name is incorrect
Called from Script_Set where src is incorrect (in GuiScript.cpp)
Called from idGuiScript::Execute

So again this is where it's reading from the script...

void CDownloadMenu::UpdateScreenshotItemVisibility(idUserInterface* gui)

mods[19]->screenshots = [27] { shared_ptr {filename="fms/_missionshots/previewshot_gatehouse_2014-01-29_19.23.20420.jpg" serverRelativeUrl="screenshots/gatehouse_2014-01-29_19.23.20420.jpg" } [1 strong ref] [default], shared_ptr {filename="fms/_missionshots/previewshot_gatehouse_2014-01-29_19.24.32859.jpg" serverRelativeUrl="screenshots/gatehouse_2014-01-29_19.24.32859.jpg" } [1 strong ref] [default], shared_ptr {filename="fms/_missionshots/previewshot_gatehouse_2014-01-29_19.26.03889.jpg" serverRelativeUrl="screenshots/gatehouse_2014-01-29_19.26.03889.jpg" } [1 strong ref] [default], shared_ptr {filename="fms/_missionshots/previewshot_gatehouse_2014-01-29_19.27.13786.jpg" serverRelativeUrl="screenshots/gatehouse_2014-01-29_19.27.13786.jpg" } [1 strong ref] [default], shared_ptr {filename="fms/_missionshots/previewshot_gatehouse_2014-01-29_19.29.52540.jpg" serverRelativeUrl="screenshots/gatehouse_2014-01-29_19.29.52540.jpg" } [1 strong ref] [default], shared_ptr {filename="fms/_missionshots/previewshot_gatehouse_2014-01-29_19.30.18716.jpg" serverRelativeUrl="screenshots/gatehouse_2014-01-29_19.30.18716.jpg" } [1 strong ref] [default], shared_ptr {filename="fms/_missionshots/previewshot_gatehouse_2014-01-29_19.31.04791.jpg" serverRelativeUrl="screenshots/gatehouse_2014-01-29_19.31.04791.jpg" } [1 strong ref] [default], ... }
Here the names are correct!!

Control+F screenshots

in void CDownloadMenu::UpdateNextScreenshotData(idUserInterface* gui, int nextScreenshotNum)

MissionScreenshot& screenshotInfo = *mods[missionIndex]->screenshots[nextScreenshotNum];
gui->SetStateInt("av_mission_cur_screenshot_num", nextScreenshotNum);

// Load next screenshot path, remove image extension
idStr path = screenshotInfo.filename;
path.StripFileExtension();

gui->SetStateString("av_mission_next_screenshot", path);

path = "fms/_missionshots/previewshot_gatehouse_2014-01-29_19.24.32859.jpg"
path.StripFileExtension();
gui->SetStateString("av_mission_next_screenshot", path)

Now path is "fms/_missionshots/previewshot_gatehouse_2014-01-29_19.24.32859" which is correct?

in void CDownloadMenu::PerformScreenshotStep(idUserInterface* gui, int step it's also correct

The gui script being called is titled "onStartFadeToNextScreenshot"

In idWindow::RunNamedEvent if we change:
    RunScriptList(namedEvents[i]->mEvent);

To:
    if (namedEvents[i]->mName == "onStartFadeToNextScreenshot") {
    }
    else {
        RunScriptList(namedEvents[i]->mEvent);
    }

The screenshots fail to load altogether, but debugging the content of the script seems difficult

Currently i'm modifying the code to debug onStartFadeToNextScreenshot easier