https://bugs.winehq.org/show_bug.cgi?id=43651
--- Comment #2 from Adam Szmigin smidge@xsco.net --- The main difference I can see from the logs is that when loading a file from the Z: drive, the following lines appear in the log:
(the sample file I used is under /srv/media/music/unmixed/Acid House)
fixme:file:FindFirstFileExW flags not implemented 0x00000002 fixme:file:FindFirstFileExW flags not implemented 0x00000002 fixme:file:GetLongPathNameW UNC pathname L"\\?\Z:\" fixme:file:GetLongPathNameW UNC pathname L"\\?\Z:\" fixme:file:FindFirstFileExW flags not implemented 0x00000002 fixme:file:FindFirstFileExW flags not implemented 0x00000002 fixme:file:GetLongPathNameW UNC pathname L"\\?\Z:\srv" fixme:file:GetLongPathNameW UNC pathname L"\\?\Z:\srv" fixme:file:FindFirstFileExW flags not implemented 0x00000002 fixme:file:FindFirstFileExW flags not implemented 0x00000002 fixme:file:GetLongPathNameW UNC pathname L"\\?\Z:\srv\media" fixme:file:GetLongPathNameW UNC pathname L"\\?\Z:\srv\media" fixme:file:FindFirstFileExW flags not implemented 0x00000002 fixme:file:FindFirstFileExW flags not implemented 0x00000002 fixme:file:GetLongPathNameW UNC pathname L"\\?\Z:\srv\media\music" fixme:file:GetLongPathNameW UNC pathname L"\\?\Z:\srv\media\music" fixme:file:FindFirstFileExW flags not implemented 0x00000002 fixme:file:FindFirstFileExW flags not implemented 0x00000002 fixme:file:GetLongPathNameW UNC pathname L"\\?\Z:\srv\media\music\unmixed" fixme:file:GetLongPathNameW UNC pathname L"\\?\Z:\srv\media\music\unmixed" fixme:file:FindFirstFileExW flags not implemented 0x00000002 fixme:file:FindFirstFileExW flags not implemented 0x00000002 fixme:file:GetLongPathNameW UNC pathname L"\\?\Z:\srv\media\music\unmixed\Acid House" fixme:file:GetLongPathNameW UNC pathname L"\\?\Z:\srv\media\music\unmixed\Acid House" fixme:file:FindFirstFileExW flags not implemented 0x00000002
No such lines are logged when choosing a file from the C: drive. Perhaps looking at the Z: drive from Engine Prime is treated as a UNC path somehow?
Additionally, Engine Prime does not show any drive letters I have assigned besides C: and Z: - in my case I mapped M: to /srv/media. This may or may not be related.